在實踐過程中，會經常遇到陣列拼接的問題，基於numpy庫concatenate是一個非常好用的陣列操作函式。

1、concatenate((a1, a2, …), axis=0)官方文件詳解

concatenate(...)
    concatenate((a1, a2, ...), axis=0)

    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.  Default is 0.

    Returns
    -------
    res : ndarray
        The concatenated array.

    See Also
    --------
    ma.concatenate : Concatenate function
 
 that preserves input masks.
    array_split : Split an array into multiple sub-arrays of equal or
                  near-equal size.
    split : Split array into a list of multiple sub-arrays of equal size.
    hsplit : Split array into multiple sub-arrays horizontally (column wise)
    vsplit : Split array into
 
 multiple sub-arrays vertically (row wise)
    dsplit : Split array into multiple sub-arrays along the 3rd axis (depth).
    stack : Stack a sequence of arrays along a new axis.
    hstack : Stack arrays in sequence horizontally (column wise)
    vstack : Stack arrays in sequence vertically (row wise)
    dstack : Stack arrays in sequence depth wise (along third dimension)

2、Parameters引數

• 傳入的引數必須是一個多個數組的元組或者列表

• 另外需要指定拼接的方向，預設是 axis = 0，也就是說對0軸的陣列物件進行縱向的拼接（縱向的拼接沿著axis= 1方向）；注：一般axis = 0，就是對該軸向的陣列進行操作，操作方向是另外一個軸，即axis=1。

In [23]: a = np.array([[1, 2], [3, 4]])

In [24]: b = np.array([[5, 6]])

In [25]: np.concatenate((a, b), axis=0)
Out[25]:
array([[1, 2],
       [3, 4],
       [5, 6]])

• 傳入的陣列必須具有相同的形狀，這裡的相同的形狀可以滿足在拼接方向axis軸上陣列間的形狀一致即可

如果對陣列物件進行 axis= 1 軸的拼接，方向是橫向0軸，a是一個2*2維陣列，axis= 0軸為2，b是一個1*2維陣列，axis= 0 是1，兩者的形狀不等，這時會報錯

In [27]: np.concatenate((a,b),axis = 1)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-27-aa1228decc36> in <module>()
----> 1 np.concatenate((a,b),axis = 1)

ValueError: all the input array dimensions except for the concatenation axis must match exactly

將b進行轉置，得到b為2*1維陣列：

In [28]: np.concatenate((a,b.T),axis = 1)
Out[28]:
array([[1, 2, 5],
       [3, 4, 6]])