CODEWITHSUNDEEP
pythonnumpy
tuuttuut
tuuttuut

Reputation: 477

Count zero rows in 2D numpy array

How do you count the amount of zero rows of a numpy array? 

array = np.asarray([[1,1],[0,0],[1,1],[0,0],[0,0]])

-> has three rows with all zero's, hence should give 3

Took me sometime to figure out this one and also couldn't find an answer on SO

Upvotes: 6

Views: 6537

Answers (3)

kmario23
kmario23

Reputation: 61355

You can use np.all if you're sure that the rows will have all zeros.

 # number of rows which has non-zero elements
In [33]: sum(np.all(arr, axis=1))
Out[33]: 2

# invert the mask to get number of rows which has all zero as its elements
In [34]: sum(~np.all(arr, axis=1))
Out[34]: 3

Upvotes: 3

miradulo
miradulo

Reputation: 29690

You could also leverage the "truthiness" of non-zero values in an array. 

np.sum(~array.any(1))

i.e., sum the rows where none of the values in said row are truthy (and hence are all zero)

Upvotes: 8

tuuttuut
tuuttuut

Reputation: 477

import numpy as np

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

non_zero_rows = np.count_nonzero((array != 0).sum(1))   # gives 2
zero_rows = len(array) - non_zero_rows                  # gives 3

Any better solutions?

Upvotes: 1

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