numpy 基本用法

1. 矩阵相关属性

import numpy as np

# 定义一个数组
array = np.array([[1,2,3], [4,5,6]])

# 数组维度  2
print(array.ndim)

# 数组形状  (2,3)
print(array.shape)

# 数组大小  6
print(array.size)

# 数据类型  int32
print(array.dtype)

2. 定义全部为0的矩阵

import numpy as np

print(np.zeros((3,4)))

[[0. 0. 0. 0.] [0. 0. 0. 0.] [0. 0. 0. 0.]]

3. 全部为1的矩阵

import numpy as np

print(np.ones((3,4), dtype=np.int16))

[[1 1 1 1] [1 1 1 1] [1 1 1 1]]

4. 定义有序矩阵

import numpy as np

# 三行四列
print(np.arange(12).reshape(3,4))

[[ 0 1 2 3] [ 4 5 6 7] [ 8 9 10 11]]

5. linspace 均分

import numpy as np

# 从1~10 分为5段
array = np.linspace(1,10,5)

print(array)

[ 1. 3.25 5.5 7.75 10. ]

6. 基本运算

import numpy as np

array1 = np.array([10, 20, 30, 40])
array2 = np.array([1, 2, 3, 4])

# [11 22 33 44]
print(array1 + array2)

# [ 9 18 27 36]
print(array1 - array2)

# 乘方  [ 1  4  9 16]
print(array2 ** 2)

# 判断矩阵的值  [ True  True False False]
print(array2 < 3)