efficient loop over numpy array

Question

Versions of this question have already been asked but I have not found a satisfactory answer.

Problem: given a large numpy vector, find indices of t

Answer 1

This solution using the numpy_indexed package has complexity n Log n, and is fully vectorized; so not terribly different from C performance, in all likelihood.

import numpy_indexed as npi
dpl = np.flatnonzero(npi.multiplicity(vect) > 1)