This is also how filtering works, you map a function that returns 0 or 1 over the list. Then you can call where (&) and it will give you the indices where the f

This is also how filtering works, you map a function that returns 0 or 1 over the list. Then you can call where (&) and it will give you the indices where the function evaluates true. Index by that and you'll filter a list.