Looking for the name of an effect and where it's explained

Hey everyone, I'd like to add an effect to my routine but I'm not sure where to find it. Here's how the trick works:

You have a pile of red cards and another of black cards. The spectator tells you where to put each card into each of the piles, and by the end, everything is separated. I know that's not a great explanation, so I'm attaching a photo of what the end looks like.

The final outcome looks something like this. Thanks for reading.