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(         


        

Answer 1

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]

Answer 2

Can you avoid numpy all together? List concatenation should be much faster than relying on numpy's methods. This will still work even if values needs to be a numpy array.

result = []
for sv in searchvals:
    result += [i for i in range(len(values)) if values[i] == sv]

Answer 3

Is this fast enough?

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