Try something like this:

use warnings; 
use strict; # should be used almost always
my %new_strings; # create the hash containing new values
while (<>) { # read STDIN and/or files specified on the command line
 chomp; # cut the newline symbol
 my ($first,$id) = (split ",",$_,3); # read first two columns and disc
+ard all others
 my $numeric = /(,[\d,]+)$/; # use regexp to match numeric values at t
+he end of the line
 unless (exists $new_strings{$id}) { # if this data was found the firs
+t time, initialise the value in the hash
  $new_strings{$id}="$first,$id";
 }
 $new_strings{$id}.=$numeric; # append the numeric data found
}
foreach (sort keys %new_strings) { # for each datum found in the secon
+d column, in alphabet order
 print "$new_strings{$_}\n"; # print the full string with all numeric 
+data found
}
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I hope that was understandable enough. See perlintro warnings strict perlop chomp split perlretut exists print for more.