use strict;
use warnings;

my %thingy;

while (<DATA>) {
   chomp;
   my ($index,$value) = split;
   push @{$thingy{$index}}, $value;
}

for (sort keys %thingy) {
   print "$_ ", join('-',@{$thingy{$_}}), "\n";
}

__DATA__
1 0
1 1
2 0
3 1 
4 3
4 6

[download]

jeffa

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)

In reply to (jeffa) Re: Group 2d array by jeffa
in thread Group 2d array by Anonymous Monk

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