1.3.1 索引¶

单个元素索引：一维数组、负数索引
二维数组的索引

1.3.2 切片¶

切片
跨步
索引数组: 针对多为数组的索引
索引结合切片

In [1]:

import numpy as np

In [2]:

# 一维数组索引
array1 = np.array([1,2,3,4,5])
array1

Out[2]:

array([1, 2, 3, 4, 5])

In [3]:

# 取第4个数值
array1[3]

Out[3]:

In [5]:

array1[-2]  # 倒数第2个数字

Out[5]:

In [6]:

# 二维数组
array2 = np.arange(14).reshape(2,7)
array2

Out[6]:

array([[ 0,  1,  2,  3,  4,  5,  6],
       [ 7,  8,  9, 10, 11, 12, 13]])

In [7]:

# 第一行第三列数字
array2[0,3]

Out[7]:

In [8]:

array2[0][3]

Out[8]:

In [9]:

array2[-1,-1]

Out[9]:

In [10]:

array2[0,-1]

Out[10]:

In [11]:

# 三维数组
array3 = np.arange(30).reshape(2,3,5)
array3

Out[11]:

array([[[ 0,  1,  2,  3,  4],
        [ 5,  6,  7,  8,  9],
        [10, 11, 12, 13, 14]],

       [[15, 16, 17, 18, 19],
        [20, 21, 22, 23, 24],
        [25, 26, 27, 28, 29]]])

In [12]:

array3[0,1,2]

Out[12]:

In [13]:

# 切片
array1

Out[13]:

array([1, 2, 3, 4, 5])

In [15]:

array1[0:3]   # a~b,a<=x<b

Out[15]:

array([1, 2, 3])

In [16]:

array1[2:6]

Out[16]:

array([3, 4, 5])

In [17]:

array1[2:]

Out[17]:

array([3, 4, 5])

In [20]:

array1[:-1]

Out[20]:

array([1, 2, 3, 4])

In [21]:

# 二维数组的切片
array2

Out[21]:

array([[ 0,  1,  2,  3,  4,  5,  6],
       [ 7,  8,  9, 10, 11, 12, 13]])

In [36]:

array2[0:1,:]    # 行参数、列参数

Out[36]:

array([[0, 1, 2, 3, 4, 5, 6]])

In [26]:

array2[1:,:]    # 行参数、列参数

Out[26]:

array([[ 7,  8,  9, 10, 11, 12, 13]])

In [28]:

array2[:,3:4]

Out[28]:

array([[ 3],
       [10]])

In [29]:

array2[0:,3:4]

Out[29]:

array([[ 3],
       [10]])

In [30]:

array2[1:,3:4]

Out[30]:

array([[10]])

In [35]:

array2[0:1,3:4]

Out[35]:

array([[3]])

In [32]:

# 三维数组
array3

Out[32]:

array([[[ 0,  1,  2,  3,  4],
        [ 5,  6,  7,  8,  9],
        [10, 11, 12, 13, 14]],

       [[15, 16, 17, 18, 19],
        [20, 21, 22, 23, 24],
        [25, 26, 27, 28, 29]]])

In [33]:

array3[0:1,2:,:]

Out[33]:

array([[[10, 11, 12, 13, 14]]])

In [34]:

array3[0:1,2:,:][0,0,2]

Out[34]:

In [37]:

# 索引多个数值
array1

Out[37]:

array([1, 2, 3, 4, 5])

In [38]:

array1[np.array([0,2,4])]   # 获取第1位，第3位，第5位的数值

Out[38]:

array([1, 3, 5])

In [39]:

# 二维数组
array2

Out[39]:

array([[ 0,  1,  2,  3,  4,  5,  6],
       [ 7,  8,  9, 10, 11, 12, 13]])

In [40]:

array2[np.array([0,1]),np.array([1,2])]  # 获取第1行第2列，第2行第3列数字

Out[40]:

array([1, 9])

In [ ]:

numpy基本操作

1.3.1 索引¶

1.3.2 切片¶

公告