NumPy 切片和索引

import numpy as np

a = np.arange(10)
s = slice(2,7,2)   # 从索引 2 开始到索引 7 停止，间隔为2
print (a[s])

[2  4  6]

import numpy as np

a = np.arange(10)
b = a[2:7:2]   # 从索引 2 开始到索引 7 停止，间隔为 2
print(b)

[2  4  6]

import numpy as np

a = np.arange(10)  # [0 1 2 3 4 5 6 7 8 9]
b = a[5]
print(b)

5

import numpy as np

a = np.arange(10)
print(a[2:])

[2  3  4  5  6  7  8  9]

import numpy as np

a = np.arange(10)  # [0 1 2 3 4 5 6 7 8 9]
print(a[2:5])

[2  3  4]

import numpy as np

a = np.array([[1,2,3],[3,4,5],[4,5,6]])
print(a)
# 从某个索引处开始切割
print('从数组索引 a[1:] 处开始切割')
print(a[1:])

[[1 2 3]
 [3 4 5]
 [4 5 6]]
从数组索引 a[1:] 处开始切割
[[3 4 5]
 [4 5 6]]

import numpy as np

a = np.array([[1,2,3],[3,4,5],[4,5,6]])  
print (a[...,1])   # 第2列元素
print (a[1,...])   # 第2行元素
print (a[...,1:])  # 第2列及剩下的所有元素

[2 4 5]
[3 4 5]
[[2 3]
 [4 5]
 [5 6]]