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

User · Answer

You can use numpy nonzero to find zero    gt  gt  gt  import numpy as np  gt  gt  gt  x   np array  1 0 2 0 3 0 0 4 0 5 0 6   reshape 4  3   gt  gt  gt  np nonzero x  0     this is what you want  array  0  1  1  2  2  3    array  1  0  2  0  2  1     gt  gt  gt  np nonzero x   array  0  0  1  2  3  3    array  0  2  1  1  0  2

User · Answer

I would do it the following way    gt  gt  gt  x   np array   1 0 0    0 2 0    1 1 0     gt  gt  gt  x array   1  0  0           0  2  0           1  1  0     gt  gt  gt  np nonzero x   array  0  1  2  2    array  0  1  0  1       if you want it in coordinates  gt  gt  gt  x np nonzero x   array  1  2  1  1    gt  gt  gt  np transpose np nonzero x   array   0  0           1  1           2  0           2  1

User · Answer

import numpy as np  x   np array  1 0 2 3 6   non zero arr   np extract x gt 0 x   min index   np amin non zero arr  min value   np argmin non zero arr

User · Answer

You can search for any scalar condition with    gt  gt  gt  a   np asarray  0 1 2 3 4    gt  gt  gt  a    0   or whatver array   True  False  False  False  False   dtype bool    Which will give back the array as an boolean mask of the condition

User · Answer

If you are working with a one-dimensional array there is a syntactic sugar    gt  gt  gt  x   numpy array  1 0 2 0 3 0 4 5 6 7 8    gt  gt  gt  numpy flatnonzero x    0  array  1  3  5

User · Answer

You can also use nonzero   by using it on a boolean mask of the condition  because False is also a kind of zero    gt  gt  gt  x   numpy array  1 0 2 0 3 0 4 5 6 7 8     gt  gt  gt  x  0 array  False  True  False  True  False  True  False  False  False  False  False   dtype bool    gt  gt  gt  numpy nonzero x  0  0  array  1  3  5     It s doing exactly the same as mtrw s way  but it is more related to the question

User · Answer

numpy where   is my favorite    gt  gt  gt  x   numpy array  1 0 2 0 3 0 4 5 6 7 8    gt  gt  gt  numpy where x    0  0  array  1  3  5

User · Answer

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

[python] Find indices of elements equal to zero in a NumPy array

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