python - 我对 numpy searchsorted 做错了什么？

Question

这在 numpy.searchsorted 中是一种有趣的行为。以下测试失败:

import numpy as np

a = np.ma.masked_array([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
                        17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30,
                        31, 32, 33, 0],
                       mask=[False, False, False, False, False, False, False,
                             False, False, False, False, False, False, False,
                             False, False, False, False, False, False, False,
                             False, False, False, False, False, False, False,
                             False, False, False, False, False,  True],
                       fill_value=0, dtype='uint8')

b = np.array([1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13, 14, 15, 16,
              17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 33],
             dtype='uint8')

expected = np.array([0,  1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12, 13,
                 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27,
                 28, 29, 32])

c = a.searchsorted(b)

np.testing.assert_array_equal(c, expected)

c 数组中的最后一项是 34，我不知道为什么。但类似的，它通过了:

aa = np.ma.masked_array([1, 2, 3, 4, 0],
                        mask=[False, False, False, False, True],
                        fill_value=0, dtype='uint8')

bb = np.array([1, 3, 4], dtype='uint8')

expectedd = np.array([0, 2, 3])

cc = aa.searchsorted(bb)

np.testing.assert_array_equal(cc, expectedd)

在numpy.array.searchsorted文档中，其描述如下:

Find the indices into a sorted array a such that, if the corresponding elements in v were inserted before the indices, the order of a would be preserved.

Answer 1

np.searchsorted尚不支持掩码数组( see here 获取受支持方法的列表)。

您可以通过使用 a.mask 的逆值手动索引 a 来获得预期结果，然后将结果作为第一个参数传递给 np.searchsorted :

c = np.searchsorted(a[~a.mask], b)

# or alternatively, a[~a.mask].searchsorted(b)

print(np.allclose(c, expected))
# True