I just saw the function
IndexBy in the autocomplete suggestions and I was curious to know exactly how it works. Unfortunately, there's no trace of it in the documentation. It returns
Association objects, so it must be new (or recently refurbished) in version 10.0.2
What does this function do are what syntax does it require? Does it have further perks that are not immediately obvious?
Edit: As mentioned in the comments, as an undocumented function this was liable to be removed. And, indeed, it has been removed from version 10.1.0. The good thing is, if anyone needs a function like this, there's now kguler and Mr. Wizard's implementations to choose from.