Numpy

import random
import time
import numpy as np
a = []
for i in range(100000000):
    a.append(random.random())
t1 = time.time()
sum1=sum(a)
t2=time.time()
b=np.array(a)
t4=time.time()
sum3=np.sum(b)
t5=time.time()
print(t2-t1, t5-t4)
输出：
8.297281980514526 1.7647507190704346

import numpy as np
list1 = [1,2,3,4]
oneArray = np.array(list1)
print(type(oneArray))
print(oneArray)
输出：
<class ‘numpy.ndarray‘>
[1 2 3 4]

import numpy as np
# 创建数组的多种形式
# 1. 直接传入列表的方式
t1 = np.array([1,2,3])
print(t1)
print(type(t1))

# 2. 传入range生成序列
t2 = np.array(range(10))
print(t2)
print(type(t2))

# 3. 使用numpy自带的np.arange()生成数组
t3 = np.arange(0,10,2)
print(t3)
print(type(t3))
输出：
[1 2 3]
<class ‘numpy.ndarray‘>
[0 1 2 3 4 5 6 7 8 9]
<class ‘numpy.ndarray‘>
[0 2 4 6 8]
<class ‘numpy.ndarray‘>

import numpy as np
list2 = [[1,2],[3,4],[5,6]]
twoArray = np.array(list2)
print(twoArray)
#返回数组类型
print(twoArray.ndim)
#返回数组形状
print(twoArray.shape)
#返回数组的元素个数
print(twoArray.size)
输出：
[[1 2]
 [3 4]
 [5 6]]
2
(3, 2)
6

#二维变三维
import numpy as np
four = np.array([[1,2,3],[4,5,6]])
# 修改的是原有的
four.shape = (3,2)
print(four)
print("-"*20)
# 返回一个新的数组
five = four.reshape(3,2)
print(five)
输出：
[[1 2]
 [3 4]
 [5 6]]
--------------------
[[1 2]
 [3 4]
 [5 6]]

#多维变一维

import numpy as np
four = np.array([[1,2,3],[4,5,6]])
# 将多维变成一维数组
five = four.reshape((6,),order=‘F‘)
# 默认情况下‘C’以行为主的顺序展开，‘F’(Fortran风格)意味着以列的顺序展开
six = four.flatten(order=‘F‘)
print(five)
print(six)
输出：
[1 4 2 5 3 6]
[1 4 2 5 3 6]

import numpy as np
a= np.array([9, 12, 88, 14, 25])
list_a = a.tolist()
print(list_a)
print(type(list_a))
输出：
[9, 12, 88, 14, 25]
<class ‘list‘>

import numpy as np
import random
f = np.array([1,2,3,4,5], dtype = np.int16)
# 返回数组中每个元素的字节单位长度
print(f.itemsize)
# 获取数据类型
print(f.dtype)
# 调整数据类型
f1 = f.astype(np.int64)
print(f1.dtype)
# 拓展随机生成小数
# 使用python语法，保留两位
print(round(random.random(),2))
arr = np.array([random.random() for i in range(10)]) # 取小数点后两位
print(np.round(arr,2))
输出：
2
int16
int64
0.02
[0.72 0.02 0.93 0.99 0.12 0.16 0.19 0.25 0.89 0.  ]

import numpy as np
import random
t1 = np.arange(24).reshape((6,4))
print(t1)
print("-"*20)
print(t1+2)
print("-"*20)
print(t1*2)
print("-"*20)
print(t1/2)
输出：
[[ 0  1  2  3]
 [ 4  5  6  7]
 [ 8  9 10 11]
 [12 13 14 15]
 [16 17 18 19]
 [20 21 22 23]]
--------------------
[[ 2  3  4  5]
 [ 6  7  8  9]
 [10 11 12 13]
 [14 15 16 17]
 [18 19 20 21]
 [22 23 24 25]]
--------------------
[[ 0  2  4  6]
 [ 8 10 12 14]
 [16 18 20 22]
 [24 26 28 30]
 [32 34 36 38]
 [40 42 44 46]]
--------------------
[[ 0.   0.5  1.   1.5]
 [ 2.   2.5  3.   3.5]
 [ 4.   4.5  5.   5.5]
 [ 6.   6.5  7.   7.5]
 [ 8.   8.5  9.   9.5]
 [10.  10.5 11.  11.5]]