np.concatenate() 使用说明

np.concatenate 是numpy中对array进行拼接的函数，使用方法如下所示：

import numpy as np

x1 = np.random.normal(1,1,(5,4))
x2 = np.random.normal(1,1,(3,4))

print(x1)
print(x1.shape)
print(x2)
print(x2.shape)

con = np.concatenate([x1,x2],axis=0)
print(con)
print(con.shape)

输出结果为：
[[ 2.22806658  0.15277615  2.21245262  1.63831116]
 [ 1.30131232 -1.09226289 -0.65959394  1.16066688]
 [ 1.52737722  0.84587186  1.53041503  0.4584277 ]
 [ 1.56096219  1.29506244  3.08048523  2.06008988]
 [ 1.79964236  0.95087117  1.30845477 -0.2644263 ]]
(5, 4)
[[0.89383392 1.49502055 2.90571116 1.71943997]
 [1.44451535 1.87838383 1.4763242  0.82597179]
 [0.72629108 1.42406398 1.35519112 0.58121617]]
(3, 4)
[[ 2.22806658  0.15277615  2.21245262  1.63831116]
 [ 1.30131232 -1.09226289 -0.65959394  1.16066688]
 [ 1.52737722  0.84587186  1.53041503  0.4584277 ]
 [ 1.56096219  1.29506244  3.08048523  2.06008988]
 [ 1.79964236  0.95087117  1.30845477 -0.2644263 ]
 [ 0.89383392  1.49502055  2.90571116  1.71943997]
 [ 1.44451535  1.87838383  1.4763242   0.82597179]
 [ 0.72629108  1.42406398  1.35519112  0.58121617]]
(8, 4)

axis参数为指定按照哪个维度进行拼接，上述的例子中x1为[5,4] x2为[3,4]，设置axis=0则代表着按照第一维度进行拼接，拼接后的尺寸为[8,4]除了第一维度的尺寸发生变化，其他维度不变，同时也说明，必须保证其他维度的尺寸是能对的上的，如果x1为[5,4],x2为[5,3],在这里如果还设置axis=1的话，则会报错，因为x1和x2的第二维度尺寸不相等，无法拼接。

按照axis=1的维度进行拼接，实例如下：

import numpy as np

x1 = np.random.normal(1,1,(5,4))
x2 = np.random.normal(1,1,(5,2))

print(x1)
print(x1.shape)
print(x2)
print(x2.shape)

con = np.concatenate([x1,x2],axis=1)
print(con)
print(con.shape)

输出结果如下：
[[ 1.06700795  2.49432822  0.13721596  0.86647501]
 [-0.24454185  0.83414428  2.06012125 -0.63322426]
 [ 2.01993142 -0.27599932  1.9101389   1.92564214]
 [ 0.12627442  0.97560762  2.00993226  2.02754602]
 [ 0.23883256  1.4805339  -0.83029287  1.37207756]]
(5, 4)
[[ 0.67988459  2.46464482]
 [ 1.19166015  2.16522311]
 [ 1.41193468 -0.01165058]
 [ 0.62496307  1.05706225]
 [ 0.85055712 -0.09588572]]
(5, 2)
[[ 1.06700795  2.49432822  0.13721596  0.86647501  0.67988459  2.46464482]
 [-0.24454185  0.83414428  2.06012125 -0.63322426  1.19166015  2.16522311]
 [ 2.01993142 -0.27599932  1.9101389   1.92564214  1.41193468 -0.01165058]
 [ 0.12627442  0.97560762  2.00993226  2.02754602  0.62496307  1.05706225]
 [ 0.23883256  1.4805339  -0.83029287  1.37207756  0.85055712 -0.09588572]]
(5, 6)

这个例子中的x1为[5,4],x2为[5,2]按照axis=1进行拼接，拼接后的尺寸为[5,6]