pandas（四）唯一值、值计数以及成员资格

>>> obj = Series([‘c‘,‘a‘,‘d‘,‘a‘,‘a‘,‘b‘,‘b‘,‘c‘,‘c‘])
>>> obj.unique()
array([‘c‘, ‘a‘, ‘d‘, ‘b‘], dtype=object)
>>> obj
0    c
1    a
2    d
3    a
4    a
5    b
6    b
7    c
8    c
dtype: object
>>> type(obj.unique())
<class ‘numpy.ndarray‘>#注意这里返回的不再是Series对象，而是ndarray的一维数组

>>> new_array = obj.unique()
>>> new_array
array([‘c‘, ‘a‘, ‘d‘, ‘b‘], dtype=object)
>>> new_array.sort()
>>> new_array
array([‘a‘, ‘b‘, ‘c‘, ‘d‘], dtype=object)
>>> import numpy as np
>>> new_array = obj.unique()
>>> new_array
array([‘c‘, ‘a‘, ‘d‘, ‘b‘], dtype=object)
>>> na = np.sort(new_array)
>>> na
array([‘a‘, ‘b‘, ‘c‘, ‘d‘], dtype=object)

>>> obj
0    c
1    a
2    d
3    a
4    a
5    b
6    b
7    c
8    c
dtype: object
>>> obj_c= obj.value_counts()
>>> obj_c
c    3
a    3
b    2
d    1
dtype: int64
>>> pd.value_counts(obj)#默认是降序
c    3
a    3
b    2
d    1
dtype: int64
>>> pd.value_counts(obj,sort =False)#对统计结果不排序
a    3
b    2
d    1
c    3
dtype: int64

>>> mask = obj.isin([‘a‘,‘c‘])
>>> mask
0     True
1     True
2    False
3     True
4     True
5    False
6    False
7     True
8     True
dtype: bool
>>> obj[mask]
0    c
1    a
3    a
4    a
7    c
8    c
dtype: object