pandas tutorial

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import pandas as pd
import numpy as np

Series

s = pd.Series()
s

Series([], dtype: float64)

data1 = [1, 2, 3]
data2 = np.array(data1, dtype=float)
s1 = pd.Series(data1)
s2 = pd.Series(data2)
print(s1)
print(s2)

0    1
1    2
2    3
dtype: int64
0    1.0
1    2.0
2    3.0
dtype: float64

s3 = pd.Series(data1, dtype=float)
s3

0    1.0
1    2.0
2    3.0
dtype: float64

我们可以看到，如果我们不指定dtype, 那么其会自行推断

data = np.array(['a', 'b', 'c', 'd'])
s = pd.Series(data, index=np.arange(100, 104))
s

100    a
101    b
102    c
103    d
dtype: object

利用dict来创建series

data = {'a':0, "b":1, 'c':2}
s = pd.Series(data)
s

a    0
b    1
c    2
dtype: int64

s.index

Index(['a', 'b', 'c'], dtype='object')

s = pd.Series(data, index=['b', 'c', 'd', 'a'])
s

b    1.0
c    2.0
d    NaN
a    0.0
dtype: float64

利用标量创建series

s = pd.Series(5, index=np.arange(5, 9))
s

5    5
6    5
7    5
8    5
dtype: int64

取

s = pd.Series([1, 2, 3, 4, 5], index=['a', 'b', 'c', 'd', 'e'])
s

a    1
b    2
c    3
d    4
e    5
dtype: int64

s[0], s[1], s[2]

(1, 2, 3)

s[:2], s[2:]

(a    1
 b    2
 dtype: int64, c    3
 d    4
 e    5
 dtype: int64)

s[-3:]

c    3
d    4
e    5
dtype: int64

s['a'], s['b'], s['c']

(1, 2, 3)

s[['a', 'b', 'e']]

a    1
b    2
e    5
dtype: int64

Dataframe

pandas.DataFrame(data, index, columns, dtype, copy)

df = pd.DataFrame()
df

data = [1, 2, 3, 4, 5]
df = pd.DataFrame(data)
df

data = [['Alex', 10], ['Bob', 12], ['Clarke', 13]]
df = pd.DataFrame(data, columns=['Name', 'Age'])
df

利用dict创建dataframe

data = {'Name':['Alex', 'Bob', 'Clarke'], 'Age':[10., 12., 13.]}
df = pd.DataFrame(data)
df

data = {'Name':['Alex', 'Bob', 'Clarke'], 'Age':[10., 12., 'NaN']}  #长度需要匹配
df = pd.DataFrame(data, index=['rank1', 'rank2', 'rank3'])
df

data = [{'a': 1, 'b': 2},{'a': 5, 'b': 10, 'c': 20}] #长度无需匹配
df = pd.DataFrame(data)
df

df1 = pd.DataFrame(data, index=['first', 'second'], columns=['a', 'b'])
df2 = pd.DataFrame(data, index=['first', 'second'], columns=['a', 'b1'])
print(df1)
print(df2)

        a   b
first   1   2
second  5  10
        a  b1
first   1 NaN
second  5 NaN

data = {
    'one': pd.Series([1, 2, 3], index=['a', 'b', 'c']),
    'two': pd.Series([1, 2, 3, 4.], index=['a', 'b', 'c', 'd'])
}
df = pd.DataFrame(data)
df

选择

df['one']

a    1.0
b    2.0
c    3.0
d    NaN
Name: one, dtype: float64

添加列

df['three'] = pd.Series([10, 20, 30])

df

df['three'] = pd.Series([10, 20, 30], index=['a', 'b', 'c'])
df

df['four'] = df['one'] + df['two']
df

列移除

del df['one']
df

df.pop('three')
df

行的选择， 添加， 移除

data = {'one' : pd.Series([1, 2, 3], index=['a', 'b', 'c']), 
   'two' : pd.Series([1, 2, 3, 4], index=['a', 'b', 'c', 'd'])}
df = pd.DataFrame(data)
df

df.loc['b']  # row b

one    2.0
two    2.0
Name: b, dtype: float64

df.iloc[1] # 按照0, 1, 2...的顺序选择

one    2.0
two    2.0
Name: b, dtype: float64

df[2:4]  #df[0]是错的

df = pd.DataFrame([[1, 2], [3, 4]], columns = ['a','b'])
df2 = pd.DataFrame([[5, 6], [7, 8]], columns = ['a','b'])
df = df.append(df2)  #通过append可以在数据框后面添加数据，但是需要注意的这个操作并不会改变数据本身而是返回一个副本
df

df.drop(1)  #利用drop可以依照index来删除某些行，比如1，即把index=1的行均移除， 同样也是返回一个副本

Panel

pandas.Panel(data, items, major_axis, minor_axis, dtype, copy)

items: axis=0

major_axis: axis=1

minor_axis: axis=2

data = np.random.rand(2, 4, 5)
data

array([[[0.13766405, 0.31453832, 0.51876265, 0.97380794, 0.28314695],
        [0.02942928, 0.28957222, 0.38716041, 0.67941481, 0.54108452],
        [0.84420857, 0.60339649, 0.49242029, 0.34838561, 0.91342058],
        [0.1127622 , 0.28420695, 0.22687715, 0.06842055, 0.87414373]],

       [[0.07591772, 0.86028356, 0.30468089, 0.15491769, 0.04969857],
        [0.31649918, 0.85154403, 0.73062637, 0.99916418, 0.3809675 ],
        [0.63817574, 0.81089715, 0.41390597, 0.6660661 , 0.91651907],
        [0.24497635, 0.43923643, 0.01833888, 0.98348271, 0.89717517]]])

p = pd.Panel(data)
p

C:\Ana\lib\site-packages\IPython\core\interactiveshell.py:3267: FutureWarning: 
Panel is deprecated and will be removed in a future version.
The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
Pandas provides a `.to_xarray()` method to help automate this conversion.

  exec(code_obj, self.user_global_ns, self.user_ns)





<class 'pandas.core.panel.Panel'>
Dimensions: 2 (items) x 4 (major_axis) x 5 (minor_axis)
Items axis: 0 to 1
Major_axis axis: 0 to 3
Minor_axis axis: 0 to 4

data = {'Item1' : pd.DataFrame(np.random.randn(4, 3)), 
   'Item2' : pd.DataFrame(np.random.randn(4, 2))}
p = pd.Panel(data)
p

C:\Ana\lib\site-packages\IPython\core\interactiveshell.py:3267: FutureWarning: 
Panel is deprecated and will be removed in a future version.
The recommended way to represent these types of 3-dimensional data are with a MultiIndex on a DataFrame, via the Panel.to_frame() method
Alternatively, you can use the xarray package http://xarray.pydata.org/en/stable/.
Pandas provides a `.to_xarray()` method to help automate this conversion.

  exec(code_obj, self.user_global_ns, self.user_ns)





<class 'pandas.core.panel.Panel'>
Dimensions: 2 (items) x 4 (major_axis) x 3 (minor_axis)
Items axis: Item1 to Item2
Major_axis axis: 0 to 3
Minor_axis axis: 0 to 2

p['Item1']

p.major_xs(0)

p.minor_xs(0)

p.major_axis, p.minor_axis

(RangeIndex(start=0, stop=4, step=1), RangeIndex(start=0, stop=3, step=1))

Basic Functionality

Series

s = pd.Series(np.random.rand(5), index=['a', 'b', 'c', 'd', 'e'])
s

a    0.795298
b    0.141144
c    0.125098
d    0.965541
e    0.957783
dtype: float64

s.axes  #返回index

[Index(['a', 'b', 'c', 'd', 'e'], dtype='object')]

s.dtype

dtype('float64')

s.empty  #是否为空

False

s.ndim

1

s.size

5

s.values  #以ndarray的形式返回数值

array([0.79529816, 0.14114367, 0.12509848, 0.96554135, 0.95778323])

s.head(3)  #返回前n个

a    0.795298
b    0.141144
c    0.125098
dtype: float64

s.tail(3)  #返回后n个

c    0.125098
d    0.965541
e    0.957783
dtype: float64

DataFrame

data = {"a":[1, 2, 3], 'b':['r', 'g', 'b']}
df = pd.DataFrame(data, index=['first', 'second', "third"])
df

df.T  #转置

df.axes  #有俩个Index

[Index(['first', 'second', 'third'], dtype='object'),
 Index(['a', 'b'], dtype='object')]

df.dtypes

a     int64
b    object
dtype: object

df.empty

False

df.ndim

2

df.shape

(3, 2)

df.size  #3 x 2

6

df.values  #以ndarray 的形式返回

array([[1, 'r'],
       [2, 'g'],
       [3, 'b']], dtype=object)

df.head(2)

df.tail(2)

Descriptive Statistic

#Create a Dictionary of series
d = {'Name':pd.Series(['Tom','James','Ricky','Vin','Steve','Smith','Jack',
   'Lee','David','Gasper','Betina','Andres']),
   'Age':pd.Series([25,26,25,23,30,29,23,34,40,30,51,46]),
   'Rating':pd.Series([4.23,3.24,3.98,2.56,3.20,4.6,3.8,3.78,2.98,4.80,4.10,3.65])
}

#Create a DataFrame
df = pd.DataFrame(d)
df

df.sum()  #默认是按行相加

Name      TomJamesRickyVinSteveSmithJackLeeDavidGasperBe...
Age                                                     382
Rating                                                44.92
dtype: object

df.sum()[1]

382

df.sum(1) #按列相加 居然自动避开了字符串...

0     29.23
1     29.24
2     28.98
3     25.56
4     33.20
5     33.60
6     26.80
7     37.78
8     42.98
9     34.80
10    55.10
11    49.65
dtype: float64

df.mean()

Age       31.833333
Rating     3.743333
dtype: float64

df.mean()['Age']

31.833333333333332

df.std()

Age       9.232682
Rating    0.661628
dtype: float64

1 count() Number of non-null observations

2 sum() Sum of values

3 mean() Mean of Values

4 median() Median of Values

5 mode() Mode of values

6 std() Standard Deviation of the Values

7 min() Minimum Value

8 max() Maximum Value

9 abs() Absolute Value

10 prod() Product of Values

11 cumsum() Cumulative Sum

12 cumprod() Cumulative Product

df.describe()

df.describe(include=['object'])

object: 针对字符列

number: 针对数字列

all: 针对全部

df.describe(include='all') #注意'all'不要以列表的形式传入, 否则会报错

df.describe(include='object')

绑定自定义函数 pipe, apply, applymap

pipe(func, ...) -- 作用于整个表格

apply(func, 0) -- 作用于列或者行

applymap(func) -- 作用于每个元素

df = pd.DataFrame(np.random.randn(5,3),columns=['col1','col2','col3'])
df

def adder(ele1,ele2):
    print("****")
    print(ele1)
    print("****")
    print(ele2)
    return ele1+ele2

df.pipe(adder, 2)  #可以看出，ele1 == df, ele2 == 2

****
       col1      col2      col3
0  1.363701  0.533478  1.850151
1  0.541553 -1.190178  1.204944
2  0.181793 -0.199892 -0.602374
3 -0.411247  1.978019  1.183671
4 -0.045223  1.444328 -0.121690
****
2

df2 = pd.DataFrame(np.random.randn(5,3),columns=['col1','col2','col3'])
df2

def inf_print(x):
    print(type(x))
    print("*******")
    print(x)

df2.apply(inf_print, 0)

<class 'pandas.core.series.Series'>
*******
0    0.386211
1   -1.873829
2   -0.881874
3    0.458257
4    0.177258
Name: col1, dtype: float64
<class 'pandas.core.series.Series'>
*******
0    1.297222
1   -0.007802
2   -2.026235
3   -0.590630
4   -1.843835
Name: col2, dtype: float64
<class 'pandas.core.series.Series'>
*******
0   -0.413626
1   -0.857307
2    0.540769
3    0.685780
4    0.131939
Name: col3, dtype: float64





col1    None
col2    None
col3    None
dtype: object

df2.apply(inf_print, 1)

<class 'pandas.core.series.Series'>
*******
col1    0.386211
col2    1.297222
col3   -0.413626
Name: 0, dtype: float64
<class 'pandas.core.series.Series'>
*******
col1   -1.873829
col2   -0.007802
col3   -0.857307
Name: 1, dtype: float64
<class 'pandas.core.series.Series'>
*******
col1   -0.881874
col2   -2.026235
col3    0.540769
Name: 2, dtype: float64
<class 'pandas.core.series.Series'>
*******
col1    0.458257
col2   -0.590630
col3    0.685780
Name: 3, dtype: float64
<class 'pandas.core.series.Series'>
*******
col1    0.177258
col2   -1.843835
col3    0.131939
Name: 4, dtype: float64





0    None
1    None
2    None
3    None
4    None
dtype: object

df2.apply(np.mean)  #可以知道， apply会将列(默认，如果第二个参数为1则为行)一次次传入

col1   -0.346795
col2   -0.634256
col3    0.017511
dtype: float64

df2.applymap(lambda x: x*100)

Reindex

N=20

df = pd.DataFrame({
   'A': pd.date_range(start='2016-01-01',periods=N,freq='D'),
   'x': np.linspace(0,stop=N-1,num=N),
   'y': np.random.rand(N),
   'C': np.random.choice(['Low','Medium','High'],N).tolist(),
   'D': np.random.normal(100, 10, size=(N)).tolist()
})
df

df.reindex(index=(0, 2, 5), columns=['A', 'C', 'B'])  #没有B所以会补

reindex_like

df1 = pd.DataFrame(np.random.randn(4, 4))
df2 = pd.DataFrame(np.random.randn(3, 3))
df1

df2

df1.reindex_like(df2)

插补

pad/ffill - 用前面的值填充

bfill/backfill - 用后面的值填充

nearest - 用最近的值填充

df2.reindex_like(df1, method="ffill")

df2.reindex_like(df1, method="bfill")

df2.reindex_like(df1, method="nearest")

limit

df1 = pd.DataFrame(np.random.randn(7, 7))
df2 = pd.DataFrame(np.random.randn(3, 3))
df1, df2

(          0         1         2         3         4         5         6
 0  0.592257  0.913287  1.276314  0.064212  1.338661 -0.110666 -0.459020
 1 -0.104347  0.388397 -1.822243  1.927027  0.890738  0.577283 -0.302798
 2 -0.016216 -1.101383  0.128118 -0.138639  1.642480 -1.382323 -0.835393
 3  1.411169 -0.395379 -0.412377  0.661016 -0.602245  0.558017  0.588833
 4  0.609378  0.338787 -0.858829  0.006657  1.509428 -0.283262 -0.563293
 5 -1.316789  0.152338 -1.027535  0.026238 -0.052540  1.233837 -1.028193
 6  0.992425  1.364755 -1.384109 -1.888707 -0.259932 -0.207928  0.135734,
           0         1         2
 0 -0.297591  1.019611  0.892070
 1  0.881763 -0.498356  1.708343
 2  0.123616  0.875709  0.387768)

df2.reindex_like(df1, method="ffill", limit=1)

df2.reindex_like(df1, method="ffill", limit=2)  #可以发现，limit限制了填补的最大数量

Renaming

df2

df2.rename(columns={0:'A', 1:'B', 2:'C', 3:'D'},
          index={0:'a', 1:'b', 2:'c', 3:'d'})

df2  #注意返回的是一个副本

Iteration

N=20
df = pd.DataFrame({
   'A': pd.date_range(start='2016-01-01',periods=N,freq='D'),
   'x': np.linspace(0,stop=N-1,num=N),
   'y': np.random.rand(N),
   'C': np.random.choice(['Low','Medium','High'],N).tolist(),
   'D': np.random.normal(100, 10, size=(N)).tolist()
   })
df

for col in df:
    print(col)

A
x
y
C
D

iteritems() (key, value)

for key, value in df.iteritems():
    print(key)
    print("*******")
    print(value)
    print("#######")

A
*******
0    2016-01-01
1    2016-01-02
2    2016-01-03
3    2016-01-04
4    2016-01-05
5    2016-01-06
6    2016-01-07
7    2016-01-08
8    2016-01-09
9    2016-01-10
10   2016-01-11
11   2016-01-12
12   2016-01-13
13   2016-01-14
14   2016-01-15
15   2016-01-16
16   2016-01-17
17   2016-01-18
18   2016-01-19
19   2016-01-20
Name: A, dtype: datetime64[ns]
#######
x
*******
0      0.0
1      1.0
2      2.0
3      3.0
4      4.0
5      5.0
6      6.0
7      7.0
8      8.0
9      9.0
10    10.0
11    11.0
12    12.0
13    13.0
14    14.0
15    15.0
16    16.0
17    17.0
18    18.0
19    19.0
Name: x, dtype: float64
#######
y
*******
0     0.529153
1     0.713513
2     0.751809
3     0.124047
4     0.472205
5     0.221076
6     0.231904
7     0.567697
8     0.384391
9     0.109675
10    0.681480
11    0.918687
12    0.332227
13    0.373779
14    0.412173
15    0.194842
16    0.372288
17    0.068876
18    0.391142
19    0.942600
Name: y, dtype: float64
#######
C
*******
0        Low
1        Low
2     Medium
3       High
4     Medium
5       High
6       High
7     Medium
8     Medium
9     Medium
10      High
11    Medium
12      High
13      High
14       Low
15    Medium
16       Low
17       Low
18      High
19       Low
Name: C, dtype: object
#######
D
*******
0     110.430517
1     125.401221
2     112.446846
3     108.633343
4     102.750572
5     108.208930
6     104.982321
7     117.178737
8      94.160408
9     108.560830
10    101.400936
11    102.421124
12     99.464727
13    107.219963
14     97.184597
15     96.671218
16    105.270272
17    101.112631
18    102.240937
19     92.492350
Name: D, dtype: float64
#######

iterrows() (index, series)

for index, row in df.iterrows():
    print(index)
    print("********")
    print(row)
    print("########")

0
********
A    2016-01-01 00:00:00
x                      0
y               0.529153
C                    Low
D                110.431
Name: 0, dtype: object
########
1
********
A    2016-01-02 00:00:00
x                      1
y               0.713513
C                    Low
D                125.401
Name: 1, dtype: object
########
2
********
A    2016-01-03 00:00:00
x                      2
y               0.751809
C                 Medium
D                112.447
Name: 2, dtype: object
########
3
********
A    2016-01-04 00:00:00
x                      3
y               0.124047
C                   High
D                108.633
Name: 3, dtype: object
########
4
********
A    2016-01-05 00:00:00
x                      4
y               0.472205
C                 Medium
D                102.751
Name: 4, dtype: object
########
5
********
A    2016-01-06 00:00:00
x                      5
y               0.221076
C                   High
D                108.209
Name: 5, dtype: object
########
6
********
A    2016-01-07 00:00:00
x                      6
y               0.231904
C                   High
D                104.982
Name: 6, dtype: object
########
7
********
A    2016-01-08 00:00:00
x                      7
y               0.567697
C                 Medium
D                117.179
Name: 7, dtype: object
########
8
********
A    2016-01-09 00:00:00
x                      8
y               0.384391
C                 Medium
D                94.1604
Name: 8, dtype: object
########
9
********
A    2016-01-10 00:00:00
x                      9
y               0.109675
C                 Medium
D                108.561
Name: 9, dtype: object
########
10
********
A    2016-01-11 00:00:00
x                     10
y                0.68148
C                   High
D                101.401
Name: 10, dtype: object
########
11
********
A    2016-01-12 00:00:00
x                     11
y               0.918687
C                 Medium
D                102.421
Name: 11, dtype: object
########
12
********
A    2016-01-13 00:00:00
x                     12
y               0.332227
C                   High
D                99.4647
Name: 12, dtype: object
########
13
********
A    2016-01-14 00:00:00
x                     13
y               0.373779
C                   High
D                 107.22
Name: 13, dtype: object
########
14
********
A    2016-01-15 00:00:00
x                     14
y               0.412173
C                    Low
D                97.1846
Name: 14, dtype: object
########
15
********
A    2016-01-16 00:00:00
x                     15
y               0.194842
C                 Medium
D                96.6712
Name: 15, dtype: object
########
16
********
A    2016-01-17 00:00:00
x                     16
y               0.372288
C                    Low
D                 105.27
Name: 16, dtype: object
########
17
********
A    2016-01-18 00:00:00
x                     17
y              0.0688757
C                    Low
D                101.113
Name: 17, dtype: object
########
18
********
A    2016-01-19 00:00:00
x                     18
y               0.391142
C                   High
D                102.241
Name: 18, dtype: object
########
19
********
A    2016-01-20 00:00:00
x                     19
y                 0.9426
C                    Low
D                92.4924
Name: 19, dtype: object
########

itertuples()

for row in df.itertuples():
    print(row)
    print("*********")

Pandas(Index=0, A=Timestamp('2016-01-01 00:00:00'), x=0.0, y=0.5291527485322772, C='Low', D=110.43051702923863)
*********
Pandas(Index=1, A=Timestamp('2016-01-02 00:00:00'), x=1.0, y=0.713512538332376, C='Low', D=125.40122093094763)
*********
Pandas(Index=2, A=Timestamp('2016-01-03 00:00:00'), x=2.0, y=0.7518093449140011, C='Medium', D=112.44684623090683)
*********
Pandas(Index=3, A=Timestamp('2016-01-04 00:00:00'), x=3.0, y=0.12404682661025335, C='High', D=108.63334270085768)
*********
Pandas(Index=4, A=Timestamp('2016-01-05 00:00:00'), x=4.0, y=0.47220500135853094, C='Medium', D=102.75057211144569)
*********
Pandas(Index=5, A=Timestamp('2016-01-06 00:00:00'), x=5.0, y=0.22107632396965704, C='High', D=108.20892974035311)
*********
Pandas(Index=6, A=Timestamp('2016-01-07 00:00:00'), x=6.0, y=0.23190410081052582, C='High', D=104.98232144314449)
*********
Pandas(Index=7, A=Timestamp('2016-01-08 00:00:00'), x=7.0, y=0.5676969704991909, C='Medium', D=117.17873695254926)
*********
Pandas(Index=8, A=Timestamp('2016-01-09 00:00:00'), x=8.0, y=0.38439055971010483, C='Medium', D=94.16040790153708)
*********
Pandas(Index=9, A=Timestamp('2016-01-10 00:00:00'), x=9.0, y=0.10967465769586215, C='Medium', D=108.56083032097501)
*********
Pandas(Index=10, A=Timestamp('2016-01-11 00:00:00'), x=10.0, y=0.6814801929159177, C='High', D=101.40093570017285)
*********
Pandas(Index=11, A=Timestamp('2016-01-12 00:00:00'), x=11.0, y=0.9186874162117078, C='Medium', D=102.42112353899493)
*********
Pandas(Index=12, A=Timestamp('2016-01-13 00:00:00'), x=12.0, y=0.33222699128916544, C='High', D=99.46472715055548)
*********
Pandas(Index=13, A=Timestamp('2016-01-14 00:00:00'), x=13.0, y=0.37377940932622644, C='High', D=107.21996306704972)
*********
Pandas(Index=14, A=Timestamp('2016-01-15 00:00:00'), x=14.0, y=0.41217288447139533, C='Low', D=97.1845970026168)
*********
Pandas(Index=15, A=Timestamp('2016-01-16 00:00:00'), x=15.0, y=0.19484179666549728, C='Medium', D=96.67121785562782)
*********
Pandas(Index=16, A=Timestamp('2016-01-17 00:00:00'), x=16.0, y=0.3722882537710307, C='Low', D=105.27027217632694)
*********
Pandas(Index=17, A=Timestamp('2016-01-18 00:00:00'), x=17.0, y=0.068875657049556, C='Low', D=101.11263086450178)
*********
Pandas(Index=18, A=Timestamp('2016-01-19 00:00:00'), x=18.0, y=0.3911420688006072, C='High', D=102.24093699498466)
*********
Pandas(Index=19, A=Timestamp('2016-01-20 00:00:00'), x=19.0, y=0.9425996619637542, C='Low', D=92.49235045195462)
*********

教程上说，迭代的东西是一个副本，所以对其中的元素进行更改是不会影响原数据的.

Sorting

sort_index

unsorted_df=pd.DataFrame(np.random.randn(10,2),index=[1,4,6,2,3,5,9,8,0,7],columns=['col2','col1'])
unsorted_df

unsorted_df.sort_index(ascending=False) #通过label排序

help(unsorted_df.sort_index)

Help on method sort_index in module pandas.core.frame:

sort_index(axis=0, level=None, ascending=True, inplace=False, kind='quicksort', na_position='last', sort_remaining=True, by=None) method of pandas.core.frame.DataFrame instance
    Sort object by labels (along an axis)
    
    Parameters
    ----------
    axis : index, columns to direct sorting
    level : int or level name or list of ints or list of level names
        if not None, sort on values in specified index level(s)
    ascending : boolean, default True
        Sort ascending vs. descending
    inplace : bool, default False
        if True, perform operation in-place
    kind : {'quicksort', 'mergesort', 'heapsort'}, default 'quicksort'
         Choice of sorting algorithm. See also ndarray.np.sort for more
         information.  `mergesort` is the only stable algorithm. For
         DataFrames, this option is only applied when sorting on a single
         column or label.
    na_position : {'first', 'last'}, default 'last'
         `first` puts NaNs at the beginning, `last` puts NaNs at the end.
         Not implemented for MultiIndex.
    sort_remaining : bool, default True
        if true and sorting by level and index is multilevel, sort by other
        levels too (in order) after sorting by specified level
    
    Returns
    -------
    sorted_obj : DataFrame

unsorted_df.sort_index(axis=1)

sort_value

unsorted_df = pd.DataFrame({'col1':[2,1,1,1],'col2':[1,3,2,4]})
unsorted_df

unsorted_df.sort_values(by="col1")

help(unsorted_df.sort_values)

Help on method sort_values in module pandas.core.frame:

sort_values(by, axis=0, ascending=True, inplace=False, kind='quicksort', na_position='last') method of pandas.core.frame.DataFrame instance
    Sort by the values along either axis
    
    Parameters
    ----------
    by : str or list of str
        Name or list of names to sort by.
    
        - if `axis` is 0 or `'index'` then `by` may contain index
          levels and/or column labels
        - if `axis` is 1 or `'columns'` then `by` may contain column
          levels and/or index labels
    
        .. versionchanged:: 0.23.0
           Allow specifying index or column level names.
    axis : {0 or 'index', 1 or 'columns'}, default 0
         Axis to be sorted
    ascending : bool or list of bool, default True
         Sort ascending vs. descending. Specify list for multiple sort
         orders.  If this is a list of bools, must match the length of
         the by.
    inplace : bool, default False
         if True, perform operation in-place
    kind : {'quicksort', 'mergesort', 'heapsort'}, default 'quicksort'
         Choice of sorting algorithm. See also ndarray.np.sort for more
         information.  `mergesort` is the only stable algorithm. For
         DataFrames, this option is only applied when sorting on a single
         column or label.
    na_position : {'first', 'last'}, default 'last'
         `first` puts NaNs at the beginning, `last` puts NaNs at the end
    
    Returns
    -------
    sorted_obj : DataFrame
    
    Examples
    --------
    >>> df = pd.DataFrame({
    ...     'col1' : ['A', 'A', 'B', np.nan, 'D', 'C'],
    ...     'col2' : [2, 1, 9, 8, 7, 4],
    ...     'col3': [0, 1, 9, 4, 2, 3],
    ... })
    >>> df
        col1 col2 col3
    0   A    2    0
    1   A    1    1
    2   B    9    9
    3   NaN  8    4
    4   D    7    2
    5   C    4    3
    
    Sort by col1
    
    >>> df.sort_values(by=['col1'])
        col1 col2 col3
    0   A    2    0
    1   A    1    1
    2   B    9    9
    5   C    4    3
    4   D    7    2
    3   NaN  8    4
    
    Sort by multiple columns
    
    >>> df.sort_values(by=['col1', 'col2'])
        col1 col2 col3
    1   A    1    1
    0   A    2    0
    2   B    9    9
    5   C    4    3
    4   D    7    2
    3   NaN  8    4
    
    Sort Descending
    
    >>> df.sort_values(by='col1', ascending=False)
        col1 col2 col3
    4   D    7    2
    5   C    4    3
    2   B    9    9
    0   A    2    0
    1   A    1    1
    3   NaN  8    4
    
    Putting NAs first
    
    >>> df.sort_values(by='col1', ascending=False, na_position='first')
        col1 col2 col3
    3   NaN  8    4
    4   D    7    2
    5   C    4    3
    2   B    9    9
    0   A    2    0
    1   A    1    1

df = pd.DataFrame(np.random.randn(8, 4),
index = ['a','b','c','d','e','f','g','h'], columns = ['A', 'B', 'C', 'D'])
df

df.loc[:, 'A']

a    2.539530
b   -0.278140
c    1.291831
d   -0.231592
e   -2.047005
f   -0.720743
g   -0.995131
h    0.190029
Name: A, dtype: float64

df.loc[:, ['A', 'C']]

df.loc['a':'h']

df.loc[df.loc[:, 'A'] > 0, 'A'] 

b    0.530365
c    1.760542
e    0.866758
f    1.620520
Name: A, dtype: float64

iloc()

df.iloc[:4]

df.iloc[1:5, 2:4]

import collections
p = collections.defaultdict(int)
p['A'] += 1
p['B'] += 1
p

defaultdict(int, {'A': 1, 'B': 1})

df = pd.DataFrame({'thing':['A', 'A', 'B', 'A', 'B', 'A', 'C', 'C', 'C']})
for row in df.loc[df.loc[:, 'thing']== 'D'].iterrows():
    print(1)

x = set([1, 2, 3, 1])
x

{1, 2, 3}

df2 = df.copy()
df2

df2.loc['a'][0] = 3

df3 = df['A']
df3

a   -0.235229
b    0.530365
c    1.760542
d   -0.241942
e    0.866758
f    1.620520
g   -0.236978
h   -0.046064
Name: A, dtype: float64

df3['a'] = 3
df3

a    3.000000
b    0.530365
c    1.760542
d   -0.241942
e    0.866758
f    1.620520
g   -0.236978
h   -0.046064
Name: A, dtype: float64

df3 = df.iloc[:4]
df3

df3.pop('A')

a    0.000000
b    0.530365
c    1.760542
d   -0.241942
Name: A, dtype: float64

d = {1:1, 2:2}
u = {3:3}
d.update(u)
d

{1: 1, 2: 2, 3: 3}

Wroking with Text Data

s = pd.Series(['Tom', 'William Rick', 'John', 'Alber@t', np.nan, '1234','SteveSmith'])
s

0             Tom
1    William Rick
2            John
3         Alber@t
4             NaN
5            1234
6      SteveSmith
dtype: object

s.str.lower() s.str.upper()

list(s.str)

[0      T
 1      W
 2      J
 3      A
 4    NaN
 5      1
 6      S
 dtype: object, 0      o
 1      i
 2      o
 3      l
 4    NaN
 5      2
 6      t
 dtype: object, 0      m
 1      l
 2      h
 3      b
 4    NaN
 5      3
 6      e
 dtype: object, 0    NaN
 1      l
 2      n
 3      e
 4    NaN
 5      4
 6      v
 dtype: object, 0    NaN
 1      i
 2    NaN
 3      r
 4    NaN
 5    NaN
 6      e
 dtype: object, 0    NaN
 1      a
 2    NaN
 3      @
 4    NaN
 5    NaN
 6      S
 dtype: object, 0    NaN
 1      m
 2    NaN
 3      t
 4    NaN
 5    NaN
 6      m
 dtype: object, 0    NaN
 1       
 2    NaN
 3    NaN
 4    NaN
 5    NaN
 6      i
 dtype: object, 0    NaN
 1      R
 2    NaN
 3    NaN
 4    NaN
 5    NaN
 6      t
 dtype: object, 0    NaN
 1      i
 2    NaN
 3    NaN
 4    NaN
 5    NaN
 6      h
 dtype: object, 0    NaN
 1      c
 2    NaN
 3    NaN
 4    NaN
 5    NaN
 6    NaN
 dtype: object, 0    NaN
 1      k
 2    NaN
 3    NaN
 4    NaN
 5    NaN
 6    NaN
 dtype: object]

s.str.lower()  #所以这一步实际上就是把s.str的第一个部分全部改为小写？

0             tom
1    william rick
2            john
3         alber@t
4             NaN
5            1234
6      stevesmith
dtype: object

s.str.upper()

0             TOM
1    WILLIAM RICK
2            JOHN
3         ALBER@T
4             NaN
5            1234
6      STEVESMITH
dtype: object

s.str.len()

s.str.len()  #实际上就是把每一个元素的长度弄出来

0     3.0
1    12.0
2     4.0
3     7.0
4     NaN
5     4.0
6    10.0
dtype: float64

s.str.strip()

s = pd.Series(['Tom            ', ' William Rick', 'John', 'Alber@t'])
s

0    Tom            
1       William Rick
2               John
3            Alber@t
dtype: object

s.str.strip()

0             Tom
1    William Rick
2            John
3         Alber@t
dtype: object

s.str.strip('k')

0    Tom            
1        William Ric
2               John
3            Alber@t
dtype: object

s.str.spilt()

s.str.split('o')

0    [T, m            ]
1       [ William Rick]
2               [J, hn]
3             [Alber@t]
dtype: object

s.str.split()

0              [Tom]
1    [William, Rick]
2             [John]
3          [Alber@t]
dtype: object

s.str.split(' ')

0    [Tom, , , , , , , , , , , , ]
1                [, William, Rick]
2                           [John]
3                        [Alber@t]
dtype: object

s.str.cat()

s.str.cat()

'Tom             William RickJohnAlber@t'

s.str.cat(sep='A')

'Tom            A William RickAJohnAAlber@t'

s.str.cat(sep='_____')

'Tom            _____ William Rick_____John_____Alber@t'

help(s.str.cat) #所以如果不是series之间相连接，需要通过关键词sep来传入分隔符

Help on method cat in module pandas.core.strings:

cat(others=None, sep=None, na_rep=None, join=None) method of pandas.core.strings.StringMethods instance
    Concatenate strings in the Series/Index with given separator.
    
    If `others` is specified, this function concatenates the Series/Index
    and elements of `others` element-wise.
    If `others` is not passed, then all values in the Series/Index are
    concatenated into a single string with a given `sep`.
    
    Parameters
    ----------
    others : Series, Index, DataFrame, np.ndarrary or list-like
        Series, Index, DataFrame, np.ndarray (one- or two-dimensional) and
        other list-likes of strings must have the same length as the
        calling Series/Index, with the exception of indexed objects (i.e.
        Series/Index/DataFrame) if `join` is not None.
    
        If others is a list-like that contains a combination of Series,
        np.ndarray (1-dim) or list-like, then all elements will be unpacked
        and must satisfy the above criteria individually.
    
        If others is None, the method returns the concatenation of all
        strings in the calling Series/Index.
    sep : string or None, default None
        If None, concatenates without any separator.
    na_rep : string or None, default None
        Representation that is inserted for all missing values:
    
        - If `na_rep` is None, and `others` is None, missing values in the
          Series/Index are omitted from the result.
        - If `na_rep` is None, and `others` is not None, a row containing a
          missing value in any of the columns (before concatenation) will
          have a missing value in the result.
    join : {'left', 'right', 'outer', 'inner'}, default None
        Determines the join-style between the calling Series/Index and any
        Series/Index/DataFrame in `others` (objects without an index need
        to match the length of the calling Series/Index). If None,
        alignment is disabled, but this option will be removed in a future
        version of pandas and replaced with a default of `'left'`. To
        disable alignment, use `.values` on any Series/Index/DataFrame in
        `others`.
    
        .. versionadded:: 0.23.0
    
    Returns
    -------
    concat : str or Series/Index of objects
        If `others` is None, `str` is returned, otherwise a `Series/Index`
        (same type as caller) of objects is returned.
    
    See Also
    --------
    split : Split each string in the Series/Index
    
    Examples
    --------
    When not passing `others`, all values are concatenated into a single
    string:
    
    >>> s = pd.Series(['a', 'b', np.nan, 'd'])
    >>> s.str.cat(sep=' ')
    'a b d'
    
    By default, NA values in the Series are ignored. Using `na_rep`, they
    can be given a representation:
    
    >>> s.str.cat(sep=' ', na_rep='?')
    'a b ? d'
    
    If `others` is specified, corresponding values are concatenated with
    the separator. Result will be a Series of strings.
    
    >>> s.str.cat(['A', 'B', 'C', 'D'], sep=',')
    0    a,A
    1    b,B
    2    NaN
    3    d,D
    dtype: object
    
    Missing values will remain missing in the result, but can again be
    represented using `na_rep`
    
    >>> s.str.cat(['A', 'B', 'C', 'D'], sep=',', na_rep='-')
    0    a,A
    1    b,B
    2    -,C
    3    d,D
    dtype: object
    
    If `sep` is not specified, the values are concatenated without
    separation.
    
    >>> s.str.cat(['A', 'B', 'C', 'D'], na_rep='-')
    0    aA
    1    bB
    2    -C
    3    dD
    dtype: object
    
    Series with different indexes can be aligned before concatenation. The
    `join`-keyword works as in other methods.
    
    >>> t = pd.Series(['d', 'a', 'e', 'c'], index=[3, 0, 4, 2])
    >>> s.str.cat(t, join=None, na_rep='-')
    0    ad
    1    ba
    2    -e
    3    dc
    dtype: object
    >>>
    >>> s.str.cat(t, join='left', na_rep='-')
    0    aa
    1    b-
    2    -c
    3    dd
    dtype: object
    >>>
    >>> s.str.cat(t, join='outer', na_rep='-')
    0    aa
    1    b-
    2    -c
    3    dd
    4    -e
    dtype: object
    >>>
    >>> s.str.cat(t, join='inner', na_rep='-')
    0    aa
    2    -c
    3    dd
    dtype: object
    >>>
    >>> s.str.cat(t, join='right', na_rep='-')
    3    dd
    0    aa
    4    -e
    2    -c
    dtype: object
    
    For more examples, see :ref:`here <text.concatenate>`.

s.str.get_dummies()

s.str.get_dummies()

s = pd.Series(['Tom ', ' William Rick', 'Alber@t', 'John'])
s.str.get_dummies()

所以是以DataFrame的形式来表示各个字符出现的顺序？

s.str.contains()

s.str.contains(' ')

0     True
1     True
2    False
3    False
dtype: bool

s.str.contains('o')

0     True
1    False
2    False
3     True
dtype: bool

s.str.replace()

s.str.replace('@', '$')

0             Tom 
1     William Rick
2          Alber$t
3             John
dtype: object

s.str.repeat()

s = pd.Series(['Tom ', ' William Rick', 'Alber@t', 'John', np.nan])

s.str.repeat(3)

0                               Tom Tom Tom 
1     William Rick William Rick William Rick
2                      Alber@tAlber@tAlber@t
3                               JohnJohnJohn
dtype: object

s.str.repeat([1, 2, 3, 4])

0                          Tom 
1     William Rick William Rick
2         Alber@tAlber@tAlber@t
3              JohnJohnJohnJohn
dtype: object

s.str.count(s2)

统计s2在每个元素中出现的次数(不一定要相等，被包含也是可以的)

s.str.count('m')

0    1
1    1
2    0
3    0
dtype: int64

s.str.startswith()

s.str.startswith('To')

0     True
1    False
2    False
3    False
4      NaN
dtype: object

s.str.startswith('To', na=False)

0     True
1    False
2    False
3    False
4    False
dtype: bool

s.str.find()

s.str.find('e')  # -1表示不存在, 其它的数字表示其位置

0   -1.0
1   -1.0
2    3.0
3   -1.0
4    NaN
dtype: float64

s.str.findall()

s.str.findall('e')  #？这样感觉还不如上面的好用啊

0     []
1     []
2    [e]
3     []
4    NaN
dtype: object

s.str.islower()

s.str.islower()

0    False
1    False
2    False
3    False
4      NaN
dtype: object

s.str.isupper()

s.str.isupper()

0    False
1    False
2    False
3    False
4      NaN
dtype: object

s.str.isnumeric()

s.str.isnumeric()

0    False
1    False
2    False
3    False
4      NaN
dtype: object

Option & Customization

get_option()

set_option()

reset_option()

describe_option()

option_context()

display.max_rows

display.max_columns

display.expand_frame_repr

display.max_colwidth

display.precision #精确度

get_option()

pd.get_option("display.max_rows")  #能够显示的最大行数

60

pd.get_option("display.max_columns") #能够显示的最大列数

20

set_option()

pd.set_option("display.max_rows", 10)  #设置能够显示的最大行数为10
pd.get_option("display.max_rows")   

10

s = pd.Series(np.arange(11))
s

0      0
1      1
2      2
3      3
4      4
      ..
6      6
7      7
8      8
9      9
10    10
Length: 11, dtype: int32

pd.set_option("display.max_columns", 2) #设置能够显示最大列数为2
pd.get_option("display.max_columns")

2

data = {1:np.arange(10), 2:np.arange(1, 11), 3:np.arange(2, 12)}
df = pd.DataFrame(data)
df

reset_option()

reset_option 接受一个参数，设置其属性为默认的属性

pd.reset_option("display.max_rows")
pd.reset_option("display.max_columns")

s

0      0
1      1
2      2
3      3
4      4
5      5
6      6
7      7
8      8
9      9
10    10
dtype: int32

describe_option()

打印对参数的说明

pd.describe_option("display.max_rows")

display.max_rows : int
    If max_rows is exceeded, switch to truncate view. Depending on
    `large_repr`, objects are either centrally truncated or printed as
    a summary view. 'None' value means unlimited.

    In case python/IPython is running in a terminal and `large_repr`
    equals 'truncate' this can be set to 0 and pandas will auto-detect
    the height of the terminal and print a truncated object which fits
    the screen height. The IPython notebook, IPython qtconsole, or
    IDLE do not run in a terminal and hence it is not possible to do
    correct auto-detection.
    [default: 60] [currently: 60]

option_context()

with pd.option_context("display.max_rows", 10):
    print(pd.get_option("display.max_rows"))
print(pd.get_option("display.max_rows"))

10
60

所以其实这就是一个上下文，在上下文管理器中，参数会被暂时性地调整，离开控制之后，便会回到原先的状态

统计函数

percent_change pct_change

比较每一个元素与其之前的元素的变化率

s = pd.Series([1,2,3,4,5,4])
s.pct_change()

0         NaN
1    1.000000
2    0.500000
3    0.333333
4    0.250000
5   -0.200000
dtype: float64

df = pd.DataFrame(np.random.randn(5, 2))
df

df.pct_change()

help(df.pct_change)

Help on method pct_change in module pandas.core.generic:

pct_change(periods=1, fill_method='pad', limit=None, freq=None, **kwargs) method of pandas.core.frame.DataFrame instance
    Percentage change between the current and a prior element.
    
    Computes the percentage change from the immediately previous row by
    default. This is useful in comparing the percentage of change in a time
    series of elements.
    
    Parameters
    ----------
    periods : int, default 1
        Periods to shift for forming percent change.
    fill_method : str, default 'pad'
        How to handle NAs before computing percent changes.
    limit : int, default None
        The number of consecutive NAs to fill before stopping.
    freq : DateOffset, timedelta, or offset alias string, optional
        Increment to use from time series API (e.g. 'M' or BDay()).
    **kwargs
        Additional keyword arguments are passed into
        `DataFrame.shift` or `Series.shift`.
    
    Returns
    -------
    chg : Series or DataFrame
        The same type as the calling object.
    
    See Also
    --------
    Series.diff : Compute the difference of two elements in a Series.
    DataFrame.diff : Compute the difference of two elements in a DataFrame.
    Series.shift : Shift the index by some number of periods.
    DataFrame.shift : Shift the index by some number of periods.
    
    Examples
    --------
    **Series**
    
    >>> s = pd.Series([90, 91, 85])
    >>> s
    0    90
    1    91
    2    85
    dtype: int64
    
    >>> s.pct_change()
    0         NaN
    1    0.011111
    2   -0.065934
    dtype: float64
    
    >>> s.pct_change(periods=2)
    0         NaN
    1         NaN
    2   -0.055556
    dtype: float64
    
    See the percentage change in a Series where filling NAs with last
    valid observation forward to next valid.
    
    >>> s = pd.Series([90, 91, None, 85])
    >>> s
    0    90.0
    1    91.0
    2     NaN
    3    85.0
    dtype: float64
    
    >>> s.pct_change(fill_method='ffill')
    0         NaN
    1    0.011111
    2    0.000000
    3   -0.065934
    dtype: float64
    
    **DataFrame**
    
    Percentage change in French franc, Deutsche Mark, and Italian lira from
    1980-01-01 to 1980-03-01.
    
    >>> df = pd.DataFrame({
    ...     'FR': [4.0405, 4.0963, 4.3149],
    ...     'GR': [1.7246, 1.7482, 1.8519],
    ...     'IT': [804.74, 810.01, 860.13]},
    ...     index=['1980-01-01', '1980-02-01', '1980-03-01'])
    >>> df
                    FR      GR      IT
    1980-01-01  4.0405  1.7246  804.74
    1980-02-01  4.0963  1.7482  810.01
    1980-03-01  4.3149  1.8519  860.13
    
    >>> df.pct_change()
                      FR        GR        IT
    1980-01-01       NaN       NaN       NaN
    1980-02-01  0.013810  0.013684  0.006549
    1980-03-01  0.053365  0.059318  0.061876
    
    Percentage of change in GOOG and APPL stock volume. Shows computing
    the percentage change between columns.
    
    >>> df = pd.DataFrame({
    ...     '2016': [1769950, 30586265],
    ...     '2015': [1500923, 40912316],
    ...     '2014': [1371819, 41403351]},
    ...     index=['GOOG', 'APPL'])
    >>> df
              2016      2015      2014
    GOOG   1769950   1500923   1371819
    APPL  30586265  40912316  41403351
    
    >>> df.pct_change(axis='columns')
          2016      2015      2014
    GOOG   NaN -0.151997 -0.086016
    APPL   NaN  0.337604  0.012002

s.pct_change(2)

0         NaN
1         NaN
2    2.000000
3    1.000000
4    0.666667
5    0.000000
dtype: float64

covariance

计算协方差，会自动省略NA

s1 = pd.Series(np.random.randn(10))
s2 = pd.Series(np.random.randn(10))
s1.cov(s2)

0.05172017259428779

当cov作用于DataFrame的时候，会计算列之间的协方差

frame = pd.DataFrame(np.random.randn(10, 5), columns=['a', 'b', 'c', 'd', 'e'])
frame.cov()

frame['a'].cov(frame.loc[:, 'b'])

0.11449787431144376

corrlation

计算相关系数

frame = pd.DataFrame(np.random.randn(10, 5), columns=['a', 'b', 'c', 'd', 'e'])
frame.corr()

frame['a'].corr(frame.iloc[:, 1])

0.3121378592734573

Ranking

排序

s = pd.Series(np.random.randn(5), index=list('abcde'))
s['d'] = s['b'] # so there's a tie
s

a   -2.179226
b    0.614786
c    1.801039
d    0.614786
e   -1.604162
dtype: float64

s.rank()

a    1.0
b    3.5
c    5.0
d    3.5
e    2.0
dtype: float64

window function 一块一块来，蛮有用的

.rolling()

df = pd.DataFrame(np.random.randn(10, 4),
   index = pd.date_range('1/1/2000', periods=10),
   columns = ['A', 'B', 'C', 'D'])
df

df.rolling(window=3).mean()

注意到, window=3, 所以每次的作用于是3行，后面跟的函数是mean, 所以第n行的结果是n, n-1, n-2三行的平均值，前俩行自然而然是NaN

.expanding()

df.expanding(min_periods=3).mean()

df['A'][:4].mean()

-0.37046210746336367

注意到 2000-01-03是一样的，后面的就不一样了，这是因为, min_periods=3限制了作用域最小为3行，所以n=4的时候，实际上是会把前面的4行取平均

.ewm()

滑动平均
实现方式

df

df.ewm(com=0.5, adjust=True).mean()

a = 1 / (1+0.5)
x1 = df.iloc[0, 0]
x2 = df.iloc[1, 0]
(x2 + (1-a) * x1) / (1 + 1 - a)

-0.8773265770527067

df.mean()

A   -0.060613
B   -0.110283
C   -0.134508
D   -0.143386
dtype: float64

Aggregations 花哨

df = pd.DataFrame(np.random.randn(10, 4),
   index = pd.date_range('1/1/2000', periods=10),
   columns = ['A', 'B', 'C', 'D'])
df

r = df.rolling(window=3, min_periods=1)
r

Rolling [window=3,min_periods=1,center=False,axis=0]

r.aggregate(np.sum)

r['A'].aggregate(np.sum)

2000-01-01    0.371455
2000-01-02   -1.199921
2000-01-03   -1.184314
2000-01-04   -1.791925
2000-01-05   -0.611110
2000-01-06   -0.935989
2000-01-07   -1.625096
2000-01-08   -1.011030
2000-01-09   -3.143932
2000-01-10   -3.155521
Freq: D, Name: A, dtype: float64

r[['A', 'B']].aggregate(np.sum)

r['A'].aggregate([np.sum, np.mean])

r.aggregate({'A':np.sum, 'B':np.mean})

Missing Data

df = pd.DataFrame(np.random.randn(5, 3), index=['a', 'c', 'e', 'f',
'h'],columns=['one', 'two', 'three'])

df = df.reindex(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'])
df

NaN: Not a Number

isnull() notnull()

df.isnull()

df.notnull()

关于缺失值的计算

当数据求和的时候，缺失值视为0，如果数据全为NA，那么结果也是NA, 额。。。好像还是0，修改了？

df['one'].sum()

-1.541684617991043

df = pd.DataFrame(index=[0,1,2,3,4,5],columns=['one','two'])
df

df['one'].sum()

0

清理，替换缺失值

df = pd.DataFrame(np.random.randn(3, 3), index=['a', 'c', 'e'],columns=['one',
'two', 'three'])

df = df.reindex(['a', 'b', 'c'])
df

df.fillna(0)

df  #看来上面是返回一个副本

df.fillna('haha')

前向后向替换

df = pd.DataFrame(np.random.randn(5, 3), index=['a', 'c', 'e', 'f',
'h'],columns=['one', 'two', 'three'])

df = df.reindex(['a', 'b', 'c', 'd', 'e', 'f', 'g', 'h'])
df

df.fillna(method='pad')  # 或者 method='ffill'

可以看到，会用前面的元素来替换

df.fillna(method="backfill")  #或者  method='bfill'

help(df.fillna)

Help on method fillna in module pandas.core.frame:

fillna(value=None, method=None, axis=None, inplace=False, limit=None, downcast=None, **kwargs) method of pandas.core.frame.DataFrame instance
    Fill NA/NaN values using the specified method
    
    Parameters
    ----------
    value : scalar, dict, Series, or DataFrame
        Value to use to fill holes (e.g. 0), alternately a
        dict/Series/DataFrame of values specifying which value to use for
        each index (for a Series) or column (for a DataFrame). (values not
        in the dict/Series/DataFrame will not be filled). This value cannot
        be a list.
    method : {'backfill', 'bfill', 'pad', 'ffill', None}, default None
        Method to use for filling holes in reindexed Series
        pad / ffill: propagate last valid observation forward to next valid
        backfill / bfill: use NEXT valid observation to fill gap
    axis : {0 or 'index', 1 or 'columns'}
    inplace : boolean, default False
        If True, fill in place. Note: this will modify any
        other views on this object, (e.g. a no-copy slice for a column in a
        DataFrame).
    limit : int, default None
        If method is specified, this is the maximum number of consecutive
        NaN values to forward/backward fill. In other words, if there is
        a gap with more than this number of consecutive NaNs, it will only
        be partially filled. If method is not specified, this is the
        maximum number of entries along the entire axis where NaNs will be
        filled. Must be greater than 0 if not None.
    downcast : dict, default is None
        a dict of item->dtype of what to downcast if possible,
        or the string 'infer' which will try to downcast to an appropriate
        equal type (e.g. float64 to int64 if possible)
    
    See Also
    --------
    interpolate : Fill NaN values using interpolation.
    reindex, asfreq
    
    Returns
    -------
    filled : DataFrame
    
    Examples
    --------
    >>> df = pd.DataFrame([[np.nan, 2, np.nan, 0],
    ...                    [3, 4, np.nan, 1],
    ...                    [np.nan, np.nan, np.nan, 5],
    ...                    [np.nan, 3, np.nan, 4]],
    ...                    columns=list('ABCD'))
    >>> df
         A    B   C  D
    0  NaN  2.0 NaN  0
    1  3.0  4.0 NaN  1
    2  NaN  NaN NaN  5
    3  NaN  3.0 NaN  4
    
    Replace all NaN elements with 0s.
    
    >>> df.fillna(0)
        A   B   C   D
    0   0.0 2.0 0.0 0
    1   3.0 4.0 0.0 1
    2   0.0 0.0 0.0 5
    3   0.0 3.0 0.0 4
    
    We can also propagate non-null values forward or backward.
    
    >>> df.fillna(method='ffill')
        A   B   C   D
    0   NaN 2.0 NaN 0
    1   3.0 4.0 NaN 1
    2   3.0 4.0 NaN 5
    3   3.0 3.0 NaN 4
    
    Replace all NaN elements in column 'A', 'B', 'C', and 'D', with 0, 1,
    2, and 3 respectively.
    
    >>> values = {'A': 0, 'B': 1, 'C': 2, 'D': 3}
    >>> df.fillna(value=values)
        A   B   C   D
    0   0.0 2.0 2.0 0
    1   3.0 4.0 2.0 1
    2   0.0 1.0 2.0 5
    3   0.0 3.0 2.0 4
    
    Only replace the first NaN element.
    
    >>> df.fillna(value=values, limit=1)
        A   B   C   D
    0   0.0 2.0 2.0 0
    1   3.0 4.0 NaN 1
    2   NaN 1.0 NaN 5
    3   NaN 3.0 NaN 4

丢弃缺失数据

我们可以利用dropna来舍弃缺失数据所在的轴(默认为行)

df.dropna()

df = pd.DataFrame({'one':np.arange(10), 'two':np.arange(10), 'three':np.arange(10)})
df.iloc[1, 2] = np.nan
df

df.dropna(axis=1)

替换数据 .replace()

df = pd.DataFrame({'one':[10,20,30,40,50,2000], 'two':[1000,0,30,40,50,60]})
df

df.replace({1000:10, 2000:66})

help(df.replace)

Help on method replace in module pandas.core.frame:

replace(to_replace=None, value=None, inplace=False, limit=None, regex=False, method='pad') method of pandas.core.frame.DataFrame instance
    Replace values given in `to_replace` with `value`.
    
    Values of the DataFrame are replaced with other values dynamically.
    This differs from updating with ``.loc`` or ``.iloc``, which require
    you to specify a location to update with some value.
    
    Parameters
    ----------
    to_replace : str, regex, list, dict, Series, int, float, or None
        How to find the values that will be replaced.
    
        * numeric, str or regex:
    
            - numeric: numeric values equal to `to_replace` will be
              replaced with `value`
            - str: string exactly matching `to_replace` will be replaced
              with `value`
            - regex: regexs matching `to_replace` will be replaced with
              `value`
    
        * list of str, regex, or numeric:
    
            - First, if `to_replace` and `value` are both lists, they
              **must** be the same length.
            - Second, if ``regex=True`` then all of the strings in **both**
              lists will be interpreted as regexs otherwise they will match
              directly. This doesn't matter much for `value` since there
              are only a few possible substitution regexes you can use.
            - str, regex and numeric rules apply as above.
    
        * dict:
    
            - Dicts can be used to specify different replacement values
              for different existing values. For example,
              ``{'a': 'b', 'y': 'z'}`` replaces the value 'a' with 'b' and
              'y' with 'z'. To use a dict in this way the `value`
              parameter should be `None`.
            - For a DataFrame a dict can specify that different values
              should be replaced in different columns. For example,
              ``{'a': 1, 'b': 'z'}`` looks for the value 1 in column 'a'
              and the value 'z' in column 'b' and replaces these values
              with whatever is specified in `value`. The `value` parameter
              should not be ``None`` in this case. You can treat this as a
              special case of passing two lists except that you are
              specifying the column to search in.
            - For a DataFrame nested dictionaries, e.g.,
              ``{'a': {'b': np.nan}}``, are read as follows: look in column
              'a' for the value 'b' and replace it with NaN. The `value`
              parameter should be ``None`` to use a nested dict in this
              way. You can nest regular expressions as well. Note that
              column names (the top-level dictionary keys in a nested
              dictionary) **cannot** be regular expressions.
    
        * None:
    
            - This means that the `regex` argument must be a string,
              compiled regular expression, or list, dict, ndarray or
              Series of such elements. If `value` is also ``None`` then
              this **must** be a nested dictionary or Series.
    
        See the examples section for examples of each of these.
    value : scalar, dict, list, str, regex, default None
        Value to replace any values matching `to_replace` with.
        For a DataFrame a dict of values can be used to specify which
        value to use for each column (columns not in the dict will not be
        filled). Regular expressions, strings and lists or dicts of such
        objects are also allowed.
    inplace : boolean, default False
        If True, in place. Note: this will modify any
        other views on this object (e.g. a column from a DataFrame).
        Returns the caller if this is True.
    limit : int, default None
        Maximum size gap to forward or backward fill.
    regex : bool or same types as `to_replace`, default False
        Whether to interpret `to_replace` and/or `value` as regular
        expressions. If this is ``True`` then `to_replace` *must* be a
        string. Alternatively, this could be a regular expression or a
        list, dict, or array of regular expressions in which case
        `to_replace` must be ``None``.
    method : {'pad', 'ffill', 'bfill', `None`}
        The method to use when for replacement, when `to_replace` is a
        scalar, list or tuple and `value` is ``None``.
    
        .. versionchanged:: 0.23.0
            Added to DataFrame.
    
    See Also
    --------
    DataFrame.fillna : Fill NA values
    DataFrame.where : Replace values based on boolean condition
    Series.str.replace : Simple string replacement.
    
    Returns
    -------
    DataFrame
        Object after replacement.
    
    Raises
    ------
    AssertionError
        * If `regex` is not a ``bool`` and `to_replace` is not
          ``None``.
    TypeError
        * If `to_replace` is a ``dict`` and `value` is not a ``list``,
          ``dict``, ``ndarray``, or ``Series``
        * If `to_replace` is ``None`` and `regex` is not compilable
          into a regular expression or is a list, dict, ndarray, or
          Series.
        * When replacing multiple ``bool`` or ``datetime64`` objects and
          the arguments to `to_replace` does not match the type of the
          value being replaced
    ValueError
        * If a ``list`` or an ``ndarray`` is passed to `to_replace` and
          `value` but they are not the same length.
    
    Notes
    -----
    * Regex substitution is performed under the hood with ``re.sub``. The
      rules for substitution for ``re.sub`` are the same.
    * Regular expressions will only substitute on strings, meaning you
      cannot provide, for example, a regular expression matching floating
      point numbers and expect the columns in your frame that have a
      numeric dtype to be matched. However, if those floating point
      numbers *are* strings, then you can do this.
    * This method has *a lot* of options. You are encouraged to experiment
      and play with this method to gain intuition about how it works.
    * When dict is used as the `to_replace` value, it is like
      key(s) in the dict are the to_replace part and
      value(s) in the dict are the value parameter.
    
    Examples
    --------
    
    **Scalar `to_replace` and `value`**
    
    >>> s = pd.Series([0, 1, 2, 3, 4])
    >>> s.replace(0, 5)
    0    5
    1    1
    2    2
    3    3
    4    4
    dtype: int64
    
    >>> df = pd.DataFrame({'A': [0, 1, 2, 3, 4],
    ...                    'B': [5, 6, 7, 8, 9],
    ...                    'C': ['a', 'b', 'c', 'd', 'e']})
    >>> df.replace(0, 5)
       A  B  C
    0  5  5  a
    1  1  6  b
    2  2  7  c
    3  3  8  d
    4  4  9  e
    
    **List-like `to_replace`**
    
    >>> df.replace([0, 1, 2, 3], 4)
       A  B  C
    0  4  5  a
    1  4  6  b
    2  4  7  c
    3  4  8  d
    4  4  9  e
    
    >>> df.replace([0, 1, 2, 3], [4, 3, 2, 1])
       A  B  C
    0  4  5  a
    1  3  6  b
    2  2  7  c
    3  1  8  d
    4  4  9  e
    
    >>> s.replace([1, 2], method='bfill')
    0    0
    1    3
    2    3
    3    3
    4    4
    dtype: int64
    
    **dict-like `to_replace`**
    
    >>> df.replace({0: 10, 1: 100})
         A  B  C
    0   10  5  a
    1  100  6  b
    2    2  7  c
    3    3  8  d
    4    4  9  e
    
    >>> df.replace({'A': 0, 'B': 5}, 100)
         A    B  C
    0  100  100  a
    1    1    6  b
    2    2    7  c
    3    3    8  d
    4    4    9  e
    
    >>> df.replace({'A': {0: 100, 4: 400}})
         A  B  C
    0  100  5  a
    1    1  6  b
    2    2  7  c
    3    3  8  d
    4  400  9  e
    
    **Regular expression `to_replace`**
    
    >>> df = pd.DataFrame({'A': ['bat', 'foo', 'bait'],
    ...                    'B': ['abc', 'bar', 'xyz']})
    >>> df.replace(to_replace=r'^ba.$', value='new', regex=True)
          A    B
    0   new  abc
    1   foo  new
    2  bait  xyz
    
    >>> df.replace({'A': r'^ba.$'}, {'A': 'new'}, regex=True)
          A    B
    0   new  abc
    1   foo  bar
    2  bait  xyz
    
    >>> df.replace(regex=r'^ba.$', value='new')
          A    B
    0   new  abc
    1   foo  new
    2  bait  xyz
    
    >>> df.replace(regex={r'^ba.$':'new', 'foo':'xyz'})
          A    B
    0   new  abc
    1   xyz  new
    2  bait  xyz
    
    >>> df.replace(regex=[r'^ba.$', 'foo'], value='new')
          A    B
    0   new  abc
    1   new  new
    2  bait  xyz
    
    Note that when replacing multiple ``bool`` or ``datetime64`` objects,
    the data types in the `to_replace` parameter must match the data
    type of the value being replaced:
    
    >>> df = pd.DataFrame({'A': [True, False, True],
    ...                    'B': [False, True, False]})
    >>> df.replace({'a string': 'new value', True: False})  # raises
    Traceback (most recent call last):
        ...
    TypeError: Cannot compare types 'ndarray(dtype=bool)' and 'str'
    
    This raises a ``TypeError`` because one of the ``dict`` keys is not of
    the correct type for replacement.
    
    Compare the behavior of ``s.replace({'a': None})`` and
    ``s.replace('a', None)`` to understand the pecularities
    of the `to_replace` parameter:
    
    >>> s = pd.Series([10, 'a', 'a', 'b', 'a'])
    
    When one uses a dict as the `to_replace` value, it is like the
    value(s) in the dict are equal to the `value` parameter.
    ``s.replace({'a': None})`` is equivalent to
    ``s.replace(to_replace={'a': None}, value=None, method=None)``:
    
    >>> s.replace({'a': None})
    0      10
    1    None
    2    None
    3       b
    4    None
    dtype: object
    
    When ``value=None`` and `to_replace` is a scalar, list or
    tuple, `replace` uses the method parameter (default 'pad') to do the
    replacement. So this is why the 'a' values are being replaced by 10
    in rows 1 and 2 and 'b' in row 4 in this case.
    The command ``s.replace('a', None)`` is actually equivalent to
    ``s.replace(to_replace='a', value=None, method='pad')``:
    
    >>> s.replace('a', None)
    0    10
    1    10
    2    10
    3     b
    4     b
    dtype: object

df = pd.DataFrame({'one':np.arange(10), 'two':np.arange(2, 12)})
df

df.replace(r'4', 'haha', regex=True)

s = pd.Series(['1', '2', '3'])
s

0    1
1    2
2    3
dtype: object

s.replace(r'3', 4, regex=True)

0    1
1    2
2    4
dtype: object

df = pd.DataFrame({'A': ['bat', 'foo', 'bait'],
             'B': ['abc', 'bar', 'xyz']})
df

df.replace(r'ba', 'new', regex=True)

看来只有str才能用regex

pandas tutorial

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原文地址：https://www.cnblogs.com/MTandHJ/p/11632540.html