Index mapping between two sorted partially overlapping numpy arrays

Question

I want to solve something like the problem detailed at Find index mapping between two numpy arrays, but where the two arrays do not necessarily contain the same set of values, a

Answer 1

Use the searchsorted indices to do a check on matches and then mask the invalid ones with the invalid-specifier. For the matching check, do b[idx]==a with idx as those indices. Hence -

invalid_specifier = -1
idx = np.searchsorted(b,a)
idx[idx==len(b)] = 0
out = np.where(b[idx]==a, idx, invalid_specifier)