A simple utility function that checks to see if an array contains multiple keys.
A simple utility function that enables recursive filtering of multi-dimensional arrays.
Easily fetch deeply nested data from a heterogenous multi-dimensional collection in PHP using dot notation... or whatever that means.
Two utility functions you will definitely want to add to your arsenal are array_keys_whitelist() and array_keys_blacklist().
Occasionally, you may need to arbitrarily reindex an array of data in PHP. WordPress doesn't really provide a function for doing this, so I put together this code snippet.