Find the indices of the values common in two arrays or lists in Python

Question

How to find the indices of common elements in two lists?

E.g. In the following two lists, [3,4] are common in 'a' and 'b'. How to find the indices of [3,4] in lists 'a' and 'b' in pythonic way?

>>> a=[1, 2, 4, 3]
>>> b=[3,4,5,6]

Answer 1

You can use function intersect1d() of Numpy with parameter return_indices=True. This function will return the common elements along with their indices in both lists.

>>> a=[1, 2, 4, 3]
>>> b=[3,4,5,6]

>>> ab,a_ind,b_ind=np.intersect1d(a,b, return_indices=True)
>>> ab
array([3, 4])
>>> a_ind
array([3, 2], dtype=int64)
>>> b_ind
array([0, 1], dtype=int64)