Determine the shuffled indices of two lists/arrays

Question

As a challenge, I\'ve given myself this problem:

Given 2 lists, A, and B, where B is a shuffled version of A, the idea is to figure out the shuffled indices.

Answer 1

We can make use of np.searchsorted with its optional sorter argument -

sidx = np.argsort(B)
out = sidx[np.searchsorted(B,A, sorter=sidx)]

Sample run -

In [19]: A = [10, 40, 30, 2, 40]
    ...: B = [30, 2, 10, 40]
    ...: 

In [20]: sidx = np.argsort(B)

In [21]: sidx[np.searchsorted(B,A, sorter=sidx)]
Out[21]: array([2, 3, 0, 1, 3])