如何同时切穿阵列的两个轴？

Question

问题： x是一个n维数组，形状为(100, 50, 50, 2)。我想以矢量化方式修改第一个和第二个轴中具有相同索引的数组元素。没有向量化，我可以用：

for i in range(50): x[:, i, i, :] = 0

问题与访问第 1 轴和第 2 轴定义的对角线的 元素相同。

此问题已在 . However, the only answer there uses the function numpy.lib.stride_tricks 中提出。根据 numpy 文档，此函数“可以指向无效内存并可能损坏结果或使程序崩溃”和“建议尽可能避免使用 as_strided”。由于这些原因，我想知道是否有更安全、更简单的方法来实现这个问题。

Answer 1

您可以使用 np.arange(50) 作为两个位置的索引；它将给出对 (0, 0), (1, 1), ..., (49, 49) 作为这两个位置的索引：

n = np.arange(x.shape[2])
x[:, n, n, :] = 0

示例：

>>> a = np.arange(150).reshape(3, 5, 5, 2)
>>> n = np.arange(a.shape[2])
>>> a[:, n, n, :] = 0
>>> a

array([[[[  0,   0],               # changed
         [  2,   3],
         [  4,   5],
         [  6,   7],
         [  8,   9]],

        [[ 10,  11],
         [  0,   0],               # changed
         [ 14,  15],
         [ 16,  17],
         [ 18,  19]],

        [[ 20,  21],
         [ 22,  23],
         [  0,   0],               # changed
         [ 26,  27],
         [ 28,  29]],

        [[ 30,  31],
         [ 32,  33],
         [ 34,  35],
         [  0,   0],               # changed
         [ 38,  39]],

        [[ 40,  41],
         [ 42,  43],
         [ 44,  45],
         [ 46,  47],
         [  0,   0]]],             # changed


       [[[  0,   0],               # changed
         [ 52,  53],
         [ 54,  55],
         [ 56,  57],
         [ 58,  59]],

        [[ 60,  61],
         [  0,   0],               # changed
         [ 64,  65],
         [ 66,  67],
         [ 68,  69]],

        [[ 70,  71],
         [ 72,  73],
         [  0,   0],               # changed
         [ 76,  77],
         [ 78,  79]],

        [[ 80,  81],
         [ 82,  83],
         [ 84,  85],
         [  0,   0],               # changed
         [ 88,  89]],

        [[ 90,  91],
         [ 92,  93],
         [ 94,  95],
         [ 96,  97],
         [  0,   0]]],             # changed


       [[[  0,   0],               # changed
         [102, 103],
         [104, 105],
         [106, 107],
         [108, 109]],

        [[110, 111],
         [  0,   0],               # changed
         [114, 115],
         [116, 117],
         [118, 119]],

        [[120, 121],
         [122, 123],
         [  0,   0],               # changed
         [126, 127],
         [128, 129]],

        [[130, 131],
         [132, 133],
         [134, 135],
         [  0,   0],               # changed
         [138, 139]],

        [[140, 141],
         [142, 143],
         [144, 145],
         [146, 147],
         [  0,   0]]]])            # changed

如何同时切穿阵列的两个轴？

How to slice through two axis of an array simultaneously?

python

vectorization

slice

diagonal

numpy-ndarray