Numpy数组拼接和分裂

1.数组的拼接

import numpy as np
1.横着拼
>> x = np.array([1,2,3])
>> y = np.array([3,2,1])
>> np.concatenate([x,y])
array([1, 2, 3, 3, 2, 1])
>> z = [99,99,99]
>> print(np.concatenate([x,y,z]))
[ 1  2  3  3  2  1 99 99 99]



2.二维数组拼接,沿着第一个轴拼接
>> grid = np.array([[1,2,3],[4,5,6]])
>> np.concatenate([grid,grid])
array([[1, 2, 3],
         [4, 5, 6],
         [1, 2, 3],
         [4, 5, 6]])



3.二维数组拼接,沿着第二个轴拼接
np.concatenate([grid,grid],axis = 1)
>> array([[1, 2, 3, 1, 2, 3],
          [4, 5, 6, 4, 5, 6]])



4.垂直拼接 vertically 垂直地 [ˈvɜrtɪkli]
>> x = np.array([1,2,3])
>> grid = np.array([[9,8,7],[6,5,4]])
>> np.vstack([x,grid])
array([[1, 2, 3],
       [9, 8, 7],
       [6, 5, 4]])



5.水平拼接  horizontally  水平地  [ˌhɔːrɪˈzɑːntəli]
>> grid = np.array([[9, 8, 7],
                 [6, 5, 4]])
>> y = np.array([[99],[99]])
>> np.hstack([grid,y])
array([[ 9,  8,  7, 99],
       [ 6,  5,  4, 99]])

2. 数组的分裂

与拼接的过程相反，可以通过np.split、np.hsplit、np.vsplit

>> x = [1,2,3,99,99,3,2,1]
>> x1,x2,x3 = np.split(x,[3,5])
array([1, 2, 3]), array([99, 99]), array([3, 2, 1])

>> grid = np.arange(16).reshape(4,4)
>> upper,lower = np.vsplit(grid,[2])

array([[0, 1, 2, 3],
        [4, 5, 6, 7]])
array([[ 8,  9, 10, 11],
        [12, 13, 14, 15]])


>> left,right = np.hsplit(grid,[2])
array([[ 0,  1],
        [ 4,  5],
        [ 8,  9],
        [12, 13]])
array([[ 2,  3],
        [ 6,  7],
        [10, 11],
        [14, 15]])