Re: how to get top N distinct elements from range?

[bearophile]

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);
}

void main() {
    immutable data = [1, 0, 0, 0, 0, 3, 3, 0, 3, 3, 0, 2, 3, 2, 
3, 2,
                      3, 1, 1, 3, 2, 1, 0, 0, 0, 1, 0, 3, 0, 3];
    foreach (i; 0 .. 6)
        data.firstDistinct(i).writeln;
}


Bye,
bearophile