how to get top N distinct elements from range?

[Chris Cain]

On Friday, 8 March 2013 at 18:17:22 UTC, bearophile wrote:
>> Otherwise return an impure take of a filter closure from a 
>> function that keeps the set. Something like (untested):
>
> It seems to work:
>
>
>
> import std.stdio, std.range, std.algorithm, std.traits;
>
> auto firstDistinct(Range)(Range r, in size_t n) {
>     bool[ForeachType!Range] mySet;
>
>     return r.filter!((k) {
>         if (k in mySet)
>             return false;
>         mySet[k] = true;
>         return true;
>     }).take(n);
> }
>

I have to say, that's a great example of beautiful simplicity in 
programming. Bravo.