Yes, thank you very much! I did actually use ELISHEVAS golf code as a basis for my own, now I'll review. As mentioned elsewhere in this thread, I don't like the C style loops, which was one of the reasons I picked it. My version was something like this:

    my %out;
    my @in = @{ $in };
    my $i = 0;
    while ( $i < $#in ) {
        push( @{ $out{ $in[ $i++ ] } }, $in[ $i++ ] ) ;
    }
    return \%out;
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Which was basically ELISHIVAS, with dereferencing and no postfix while.