Re: C# to D

[Dennis Ritchie via Digitalmars-d-learn]

On Wednesday, 25 March 2015 at 20:09:53 UTC, bearophile wrote:

This is still not very efficient (perhaps the last sorting has to be stable):

void main() {
    import std.stdio, std.algorithm, std.typecons, std.array;

[7, 5, 7, 3, 3, 5, 3, 3, 0, 3, 1, 1, 5, 1, 1, 1, 2, 2, 8, 5, 8, 8]

    .sort()
    .groupBy!((a, b) => a == b)
    .map!array
    .array
    .sort!q{a.length > b.length}
    .joiner
    .writeln;
}

On Wednesday, 25 March 2015 at 20:53:43 UTC, Ivan Kazmenko wrote:

5. An efficient version would be to count the integers by using an associative array (or a redBlackTree for guaranteed upper bound) and then use these. It is O (n) time and memory spent in precalculation phase and O (n log n) time for sorting. Looks like there is no way to write that as a chain of transforms, but many optimizations do require manual labor.

-----
import std.algorithm, std.conv, std.range, std.stdio;
void main () {
    auto arr = [7, 5, 7, 3, 3, 5, 3, 3, 0, 3, 1, 1, 5, 1,
1, 1, 2, 2, 8, 5, 8, 8];
    int [int] counts;
    foreach (e; arr) {
        counts[e]++;
    }

arr.multiSort !((a, b) => counts[a] > counts[b], (a, b) => a < b);

    arr.map !(to !(string))
        .join (" ")
        .writeln;
    // prints 1 1 1 1 1 3 3 3 3 3 5 5 5 5 8 8 8 2 2 7 7 0
}
-----

Thank you very much, Ivan and bearophile!

On Wednesday, 25 March 2015 at 20:53:43 UTC, Ivan Kazmenko wrote:

Also, some of my previously posted codes do not compile under 2.066 or earlier unless you replace .join (' ') with .join (" ") there.

I have long been updated :)