How to find the set of indices where two vectors have equal elements in Python

Question

I have two vectors in Python: Predictions and Labels. What I would like to do is to find out the set of indices where these two vectors have equal elements. For example, lets say the vectors are:

Predictions = [4, 2, 5, 8, 3, 4, 2, 2]

     Labels = [4, 3, 4, 8, 2, 2, 1, 2]

So the set of indices where the two vectors have equal elements would be:

Indices = [0, 3, 7]

How can I get this in Python? Without using for-loops etc. Is there a built-in function for example in numpy?

Thank you for any help!

Answer 1

This is one way of doing it with numpy:

np.where(np.equal(Predictions, Labels))

which is equivalent to:

np.equal(Predictions, Labels).nonzero()

It will return a single element tuple though, so to get the actual array, add [0] as in:

np.equal(Predictions, Labels).nonzero()[0]