C# to D

[Ivan Kazmenko via Digitalmars-d-learn]

On Wednesday, 25 March 2015 at 20:09:53 UTC, bearophile wrote:
> Dennis Ritchie:
>
>> A more effective solution for C ++:
>>
>> #include <iostream>
>> #include <vector>
>> #include <range/v3/all.hpp>
>>
>> int main() {
>>  using namespace ranges;
>>
>>  auto rng = istream<int>( std::cin )
>>           | to_vector
>>           | action::sort
>>           | view::group_by( std::equal_to<int>() )
>>           | copy
>>           | action::stable_sort( []( const auto& e1, const 
>> auto& e2 ) { return distance( e1 ) < distance( e2 ); } );
>>  std::cout << ( rng );
>> }
>
>
> 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;
> }
>
>
> Bye,
> bearophile

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
}
-----

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