[英]Index elements from 2D array with a 2D array and change these elements according to a 1D array [Python]
[英]2d index to select elements from 1d array
我正在尝试使用 2d boolean 数组( ix
)从 1d 数组( c
)中选择元素来创建 2d 数组( r
)。 生成的二维数组也是 boolean 数组。 每列代表c
中的唯一值。
例子:
>>> ix
array([[ True, True, False, False, False, False, False],
[False, False, True, False, False, False, True],
[False, False, False, True, False, False, False]])
>>> c
array([1, 2, 3, 4, 8, 2, 4])
预期结果
1, 2, 3, 4, 8
r = [
[ True, True, False, False, False], # c[ix[0][0]] == 1 and c[ix[0][1]] == 2; it doesn't matter that ix[0][5] (pointing to `2` in `c`) is False as ix[0][1] was already True which is sufficient.
[False, False, True, True, False], # [3]
[False, False, False, True, False] # [4] as ix[2][3] is True
]
这可以以矢量化的方式完成吗?
让我们试试:
# unique values
uniques = np.unique(c)
# boolean index into each row
vals = np.tile(c,3)[ix.ravel()]
# search within the unique values
idx = np.searchsorted(uniques, vals)
# pre-populate output
out = np.full((len(ix), len(uniques)), False)
# index into the output:
out[np.repeat(np.arange(len(ix)), ix.sum(1)), idx ] = True
Output:
array([[ True, True, False, False, False],
[False, False, True, True, False],
[False, False, False, True, False]])
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