python - 将 3D Numpy 数组 reshape 为 2D 数组

Question

我在 Numpy 中有以下 3D 数组:

a = np.array([[[1,2],[3,4]], [[5,6],[7,8]], [[9,10],[11,12]],[[13,14],[15,16]]])

当我写作时

b = np.reshape(a, [4,4])

二维结果数组看起来像

 [[ 1  2  3  4]
  [ 5  6  7  8]
  [ 9 10 11 12]
  [13 14 15 16]]

但是，我希望它是这样的形状:

 [[ 1  2  5  6]
  [ 3  4  7  8]
  [ 9 10 13 14]
  [11 12 15 16]]

我怎样才能在 Python/Numpy 中有效地做到这一点？

Answer 1

reshape 以将第一个轴分成两个，置换轴和另一个 reshape -

a.reshape(2,2,2,2).transpose(0,2,1,3).reshape(4,4)
a.reshape(2,2,2,2).swapaxes(1,2).reshape(4,4)

使其通用化，将成为 -

m,n,r = a.shape
out = a.reshape(m//2,2,n,r).swapaxes(1,2).reshape(-1,2*r)

sample 运行-

In [20]: a
Out[20]: 
array([[[ 1,  2],
        [ 3,  4]],

       [[ 5,  6],
        [ 7,  8]],

       [[ 9, 10],
        [11, 12]],

       [[13, 14],
        [15, 16]]])

In [21]: a.reshape(2,2,2,2).swapaxes(1,2).reshape(4,4)
Out[21]: 
array([[ 1,  2,  5,  6],
       [ 3,  4,  7,  8],
       [ 9, 10, 13, 14],
       [11, 12, 15, 16]])