Python中的numpy模块学习

本文是基于Windows系统环境，学习和测试numpy模块：

• Windows 10

• PyCharm 2018.3.5 for Windows (exe)

• python 3.6.8 Windows x86 executable installer

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1. numpy初始化数组和矩阵

• numpy初始化一个空数组

import numpy as np
a = np.array([])
print(a.size) # size = 0

• numpy利用列表初始化一个数组

import numpy as np
a = np.array([1,2,3]) # 初始化一个3×1的向量
print(np.shape(a)) # np.shape(a)=(3,)
print(a.size) # size =3

• numpy利用列表初始化一个矩阵

import numpy as np
a = np.array([[1,2,3],[2,3,4]]) # 初始化一个2×3的矩阵
print(np.shape(a)) # np.shape(a)=(2,3)
print(a.size) # size =6

• numpy生成元素值全为0的一维数组

import numpy as np
a = np.zeros(6) # 创建长度为6的，元素都是0一维数组
print(np.shape(a)) # np.shape(a)=(6,)
print(a.size) # size =6

• numpy生成元素值全为1的一维数组

import numpy as np
a = np.ones(6) # 创建长度为6的，元素都是1一维数组
print(np.shape(a)) # np.shape(a)=(6,)
print(a.size) # size =6

2. numpy返回array中元素的index

• numpy利用argwhere()函数来实现

import numpy as np
data = np.array([[1, 2, 3], [4, 5, 6], [7, 8, 1]])
target = 1
target_index = np.argwhere(data == target)
print(target_index)  # 返回一个下标矩阵
print(np.shape(target_index))  # np.shape(target_index)=(2,2)

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