>perl -wMstrict -le
"use List::Util qw(sum);
 ;;
 my $s = 'r1y2g3g4y2r4r3y5y3g3g6g2r1';
 my $r = 'r 1 y 2 g 7 y 2 r 7 y 8 g 11 r 1 ';
 ;;
 $s =~ s{ (([[:alpha:]]) \d+ (?: \2 \d+)*) }
        {$2 ${ \sum $1 =~ /\d+/g } }xmsg;
 print qq{'$s'};
 ;;
 $s eq $r or die 'not what was wanted';
"
'r 1 y 2 g 7 y 2 r 7 y 8 g 11 r 1 '