how to get top N distinct elements from range?

[Andrea Fontana]

On Friday, 8 March 2013 at 19:36:04 UTC, bearophile wrote:
>> auto firstDistinct(Range)(Range r, in size_t n)
>> if (isInputRange!Range) {
>>    bool[ForeachType!Range] mySet;
>>
>>    return r.filter!((k) {
>>        if (k in mySet)
>>            return false;
>>        mySet[k] = true;
>>        return true;
>>    }).take(n);
>> }
>
> I think the standard library of Ada2012 has bounded containers, 
> so you can use them to stack-allocate a hash set that can 
> contain up to n items (plus some more free cells to keep its 
> load factor low enough).
>
> In Rust there are fully safe stack-allocated closures. 
> Combining the two things it's possible to create a function 
> like that firstDistinct() with zero heap allocations, that is 
> probably fast.
>
> Bye,
> bearophile

Something goes wrong by the way. I removed "n" template params 
and "take(n)" (i can do after distinct() call, isn't it the 
same?).

Try this (sorted for better reading):

iota(100).map!((x) => 
uniform(0,10))().distinct().array.sort.writeln;
iota(100).map!((x) => 
uniform(0,10))().array.distinct().array.sort.writeln;

output:
[0, 0, 3, 3, 4, 4, 4, 6, 7, 8]
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]