Numpy int array: Find indices of multiple target ints

Question

I have a large numpy array (dtype=int) and a set of numbers which I'd like to find in that array, e.g.,

import numpy as np
values = np.array([1, 2, 3, 1, 2, 4, 5, 6, 3, 2, 1])
searchvals = [3, 1]
# result = [0, 2, 3, 8, 10]

The result array doesn't have to be sorted.

Speed is an issue, and since both values and searchvals can be large,

for searchval in searchvals:
    np.where(values == searchval)[0]

doesn't cut it.

Any hints?

Answer 1

Is this fast enough?

>>> np.where(np.in1d(values, searchvals))
(array([ 0,  2,  3,  8, 10]),)

Answer 2

I would say using np.in1d would be the intuitive solution to solve such a case. Having said that, based on this solution here's an alternative with np.searchsorted -

sidx = np.argsort(searchvals)
left_idx = np.searchsorted(searchvals,values,sorter=sidx,side='left')
right_idx = np.searchsorted(searchvals,values,sorter=sidx,side='right')
out = np.where(left_idx != right_idx)[0]