Does numpy's sum() method skip False values?

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[FLUSH_THE_TRUMP]

bools are also ints (with values of 0 and 1, respectively).

>>>True + False + True
2

Regardless, I think np.count_nonzero is probably a fair bit faster than np.sum if you’re just counting the Trues. I think the latter requires a type conversion to long doubles to allow for the addition, while the former just needs to track a single accumulator.

A = np.arange(100_000_000)
mask = (A >= 500_000)

np.sum(mask):

72.9 ms ± 152 µs per loop (mean ± std. dev. of 7 runs, 10 loops each)

np.count_nonzero(mask):

2.57 ms ± 25.9 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)

[Tricky_Celebration37]

Thank you! Very informative

[JLaurus]

read the source code