groupBy predicates: unary, binary, or both?

[Andrei Alexandrescu]

On 12/29/13 2:27 AM, bearophile wrote:
> But another common need is to group by equivalent classes using an
> associative array. Both C# and Clojure have this functionality (on LINQ
> and in the functions toolkit). This means that a "hashGroup" builds an
> associative array inside and returns it.
>
>
> See also:
> http://d.puremagic.com/issues/show_bug.cgi?id=5968
> http://d.puremagic.com/issues/show_bug.cgi?id=9842

I think hash joins should come first.

Andrei