python - NumPy: Comparing Elements in Two Arrays

Question

Anyone ever come up to this problem? Let's say you have two arrays like the following

a = array([1,2,3,4,5,6])
b = array([1,4,5])

Is there a way to compare what elements in a exist in b? For example,

c = a == b # Wishful example here
print c
array([1,4,5])
# Or even better
array([True, False, False, True, True, False])

I'm trying to avoid loops as it would take ages with millions of elements. Any ideas?

Cheers

question from:https://stackoverflow.com/questions/1613249/numpy-comparing-elements-in-two-arrays

Answer 1

Actually, there's an even simpler solution than any of these:

import numpy as np

a = array([1,2,3,4,5,6])
b = array([1,4,5])

c = np.in1d(a,b)

The resulting c is then:

array([ True, False, False,  True,  True, False], dtype=bool)