How to count the number of true elements in a NumPy bool array

Question

I have a NumPy array \'boolarr\' of boolean type. I want to count the number of elements whose values are True. Is there a NumPy or Python routine dedicated for

Answer 1

You have multiple options. Two options are the following.

numpy.sum(boolarr)
numpy.count_nonzero(boolarr)

Here's an example:

>>> import numpy as np
>>> boolarr = np.array([[0, 0, 1], [1, 0, 1], [1, 0, 1]], dtype=np.bool)
>>> boolarr
array([[False, False,  True],
       [ True, False,  True],
       [ True, False,  True]], dtype=bool)

>>> np.sum(boolarr)
5

Of course, that is a bool-specific answer. More generally, you can use numpy.count_nonzero.

>>> np.count_nonzero(boolarr)
5