Filter an array in Python3 / Numpy and return indices

Question

Is there any built-in function in Python3/Numpy which filters an array and returns indices of the elements which are left? Something similar to numpy.argsort for sorting. The filter I have is setting both min and max thresholds - all values below/above min/max have to be filtered out.

I've seen Python's function filter, but I don't see a way to extract indices using it.

EDITED: Lots of useful information in the answers, thank you!

As @SvenMarnach pointed out, mask is enough:

mask = (min_value < a) & (a < max_value)

Now I have to apply this mask to other arrays of the same shape as a, but not sure what is the best way to do it...

Answer 1

The command numpy.where will return the indices of an array after you've applied a mask over them. For example:

import numpy as np
A = np.array([1,2,3,6,2])
np.where(A>2)

gives:

(array([2, 3]),)

A more complicated example:

A = np.arange(27).reshape(3,3,3)
np.where( (A>10) & (A<15) )

gives:

(array([1, 1, 1, 1]), array([0, 1, 1, 1]), array([2, 0, 1, 2]))

I'll agree with @SvenMarnach, usually you don't need the indices.