Find indices of elements equal to zero in a NumPy array


Question

NumPy has the efficient function/method nonzero() to identify the indices of non-zero elements in an ndarray object. What is the most efficient way to obtain the indices of the elements that do have a value of zero?

1
118
1/9/2018 10:29:23 PM

Accepted Answer

numpy.where() is my favorite.

>>> x = numpy.array([1,0,2,0,3,0,4,5,6,7,8])
>>> numpy.where(x == 0)[0]
array([1, 3, 5])
189
7/13/2012 6:46:34 AM

There is np.argwhere,

import numpy as np
arr = np.array([[1,2,3], [0, 1, 0], [7, 0, 2]])
np.argwhere(arr == 0)

which returns all found indices as rows:

array([[1, 0],    # Indices of the first zero
       [1, 2],    # Indices of the second zero
       [2, 1]],   # Indices of the third zero
      dtype=int64)

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