Numpy: For every element in one array, find the index in another array

Question

I have two 1D arrays, x & y, one smaller than the other. I\'m trying to find the index of every element of y in x.

I\'ve found two naive ways to do this, the fir

Answer 1

How about this?

It does assume that every element of y is in x, (and will return results even for elements that aren't!) but it is much faster.

import numpy as np

# Generate some example data...
x = np.arange(1000)
np.random.shuffle(x)
y = np.arange(100)

# Actually preform the operation...
xsorted = np.argsort(x)
ypos = np.searchsorted(x[xsorted], y)
indices = xsorted[ypos]