in reply to Adjacent numbers

I had to take a stab at this. I am not proud of having to insert the final loop to filter out repeats, but maybe someone else can fix that. ;)

This solution splits each data element by underscore and sorts by both the left and right, which hopefully will line up any stray adjacent elements and prevent having to look behind.

use strict; use warnings; my %ordered; for (<DATA>) { chomp; my ($left,$right) = split /_/, $_, 2; push @{ $ordered{$left} }, $right; } my @matches; for my $key (sort keys %ordered) { my $last = 0; for (sort @{ $ordered{$key} } ) { push @matches, "${key}_$last","${key}_$_" if $_ - $last == 1; $last = $_; } } my %seen; for (@matches) { print "$_\n" unless $seen{$_}++; } __DATA__ X_203 2L_33 3L_45 X_202 2L_34 X_204 2L_32 3L_87 3L_88


(the triplet paradiddle with high-hat)