python - 沿给定轴 1 将 numpy ndarray 与 3d 数组相加

Question

我有一个形状为 (2,3,3) 的 numpy ndarray，例如:

array([[[ 1,  2,  3],
    [ 4,  5,  6],
    [12, 34, 90]],

   [[ 4,  5,  6],
    [ 2,  5,  6],
    [ 7,  3,  4]]])

我迷失在 np.sum(高于 ndarray ，axis=1)中，为什么答案是:

array([[17, 41, 99],
   [13, 13, 16]])

谢谢

Answer 1

Axes are defined for arrays with more than one dimension. A 2-dimensional array has two corresponding axes: the first running vertically downwards across rows (axis 0), and the second running horizontally across columns (axis 1).

设 A 为数组，然后在您的示例中，当轴为 1 时，添加 [i,:,k]。同样，对于轴 0，添加 [:,j,k]，当轴为 2 时，添加 [i,j,:]。

A = np.array([
   [[ 1,  2,  3],[ 4,  5,  6], [12, 34, 90]],
   [[ 4,  5,  6],[ 2,  5,  6], [ 7,  3,  4]]
])

np.sum(A,axis = 0)
    array([[ 5,  7,  9],
           [ 6, 10, 12],
           [19, 37, 94]])
np.sum(A,axis = 1)
    array([[17, 41, 99],
           [13, 13, 16]])
np.sum(A,axis = 2)
    array([[ 6, 15,136],
           [15, 13, 14]])