numpy Mask 2d array rows by ranges from 1d array

Question

I have this 1d array which represents the ranges of valid values.

ranges = np.array([1, 2, 0])

and i have multiple 2d arrays that have values, which i want to mask by index based on the ranges above.

matrixes = np.array([[0, 1, 2],
                     [3, 4, 5],
                     [6, 7, 8]])

So each value in "ranges" represents the number of rows that have valid values in "matrixes" (the columns correspond to each-other), so the masking would return something like:

              ([[True,  True,  False],
                [False, True,  False],
                [False, False, False]])

The first column has 1 valid value, the first. The second column has 2 valid values... etc.

I tried several other topics but could not figure out how to do it... ex: How to properly mask a numpy 2D array?

mozway · Accepted Answer · 2023-04-19 06:27:56Z

1

Use broadcasting:

out = np.arange(matrixes.shape[0])[:,None]<ranges

Output:

[[ True  True False]
 [False  True False]
 [False False False]]

answered Apr 19, 2023 at 6:27

mozway

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1 Comment

Andrei M. Over a year ago

Hey, thanks for the reply. With some transposing it seems to work fine, although a bit one-line-ish :) Thank you.

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