How to use negation of isin() function of numpy to indices

Question

I have two lists. I want to find the indices of the elements in the big list which are not present in the small list. How can I use the isin() function for it?

Answer 1

You can use the negation of the isin() function to select the indices of elements in the big list that are not present in the smaller list.

Here is an example. 'a' is the big list, and 'b' is the smaller list.

>>> import numpy as np
>>> a=np.array([11,12,13,14,15,16,17])
>>> b=np.array([12,14,15,17])
>>> (~np.isin(a, b)).nonzero()[0]
array([0, 2, 5])