np.concatenate

numpy.concatenate
numpy.concatenate((a1, a2, ...), axis=0, out=None)
Join a sequence of arrays along an existing axis.

Parameters:	
a1, a2, … : sequence of array_like
The arrays must have the same shape, except in the dimension corresponding to axis (the first, by default).

axis : int, optional
The axis along which the arrays will be joined. If axis is None, arrays are flattened before use. Default is 0.

out : ndarray, optional
If provided, the destination to place the result. The shape must be correct, matching that of what concatenate would have returned if no out argument were specified.

Returns:	
res : ndarray
The concatenated array.

Join a sequence of arrays along an existing axis.
在指定的轴处，将多个数组连成一个sequence

>>> a = np.array([[1, 2], [3, 4]])
>>> b = np.array([[5, 6]])
>>> np.concatenate((a, b), axis=0)
array([[1, 2],
       [3, 4],
       [5, 6]])
>>> np.concatenate((a, b.T), axis=1)
array([[1, 2, 5],
       [3, 4, 6]])
>>> np.concatenate((a, b), axis=None)
array([1, 2, 3, 4, 5, 6])

上边这个例子可以看出，在axis = 0处，将a，b连城一个序列。axis = 0，对应着数组中的行，换句话说，就是将a，b按行摞列起来。这时候，行数会增加。

import numpy as np
a = np.array([[1, 2], [3, 4], [5, 6]])
b = np.array([[1],[2],[3]])
np.concatenate((a, b), axis = 1)
Out[5]: 
array([[1, 2, 1],
       [3, 4, 2],
       [5, 6, 3]])

这个例子，axis = 1，就是按列摞起来，这时候行数不变，列数会增加。