Depending on the platform, there's at least 2 ways to do that :-)

E.g. - "functional" is simply something like:

    subset = filter( predicate, superset )

... but on a "procedural" platform, it's a bit more challenging, starting with how much space to allocate for the result, or whether to mutate the input, and other wading through the swamp.

But, yeah, I can see how it would get people to start up talking somewhere, or else go into "deer in the headlights" mode.