python - 如何在迭代器中屏蔽除第 n 个元素之外的每个元素？

Question

我正在尝试创建一个掩码数组(或至少填充 NaN)，该数组仅提供第 n 个(示例中的第 8 个)位置的值。该数组的长度应与原始数组的长度相同。

有没有一种不那么荒谬的方法来做到这一点？

b = np.array([[i for i in 7*[np.nan] + [val]] for val in a[::8]]).flatten()[7:]

Answer 1

一种方法是使用切片分配:

>>> a
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, 30, 31, 32, 33,
       34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50,
       51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63])
>>> b = numpy.array([numpy.NaN] * len(a))
>>> b[::8] = a[::8]
>>> b
array([  0.,  nan,  nan,  nan,  nan,  nan,  nan,  nan,   8.,  nan,  nan,
        nan,  nan,  nan,  nan,  nan,  16.,  nan,  nan,  nan,  nan,  nan,
        nan,  nan,  24.,  nan,  nan,  nan,  nan,  nan,  nan,  nan,  32.,
        nan,  nan,  nan,  nan,  nan,  nan,  nan,  40.,  nan,  nan,  nan,
        nan,  nan,  nan,  nan,  48.,  nan,  nan,  nan,  nan,  nan,  nan,
        nan,  56.,  nan,  nan,  nan,  nan,  nan,  nan,  nan])