How to get indices of values of numpy array which are zero

Question

Lets say I have a numpy array as below:

array([ 1. ,  2. ,  0. ,  3.4,  0. ,  1.1])

Now I want to get indices of all the elements which are zero. Reason being I want to get those indices and then for a different array I want to convert the elements on same indices to zero.

To get indices of non zero I know we can use nonzero or argwhere.

np.nonzero(a)

(array([0, 1, 3, 5]),)

Then lets say I have array b I can use the above indices list and convert all the elements of array b with same indices to zero like below:

b[np.nonzero(a)]=0

This is fine but it is for non zero indices. How to get for zero indices.

user2357112 · Accepted Answer · 2016-06-21 21:49:18Z

4

If you just want to use the result for indexing purposes, it's more efficient to make a boolean array than an array of indices:

a == 0

You can index with that the same way you would have used the array of indices:

b[a == 0] = 0

If you really want an array of indices, you can call np.nonzero on the boolean array:

np.nonzero(a == 0)

np.where also works.

answered Jun 21, 2016 at 21:49

user2357112

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