how to get top N distinct elements from range?

[Andrea Fontana]

On Friday, 8 March 2013 at 22:36:35 UTC, Andrea Fontana wrote:
> 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]

Here the answer:

auto r=iota(100).map!((x) => uniform(0,10))();
writeln(r.front," ", r.front, " ", r.front, " ", r.front);

But i think "front" was "cached", but it seems not...