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in reply to Please help...

[tauser02@gfmwsp02lds bin]$ cat x use strict; use warnings; my %data; while (<DATA>) { my ($cluster, $unit) = split /\s+/; push(@{$data{$cluster}}, $unit); } for my $cluster (sort keys %data) { print $cluster, ' ', join(' ', @{$data{$cluster}}), "\n"; } __DATA__ Cluster1 unit1 Cluster1 unit2 Cluster1 unit3 Cluster1 unit4 Cluster1 unit5 Cluster2 unit6 Cluster2 unit7 Cluster2 unit8 Cluster2 unit9 Cluster2 unit10 [tauser02@gfmwsp02lds bin]$ perl x Cluster1 unit1 unit2 unit3 unit4 unit5 Cluster2 unit6 unit7 unit8 unit9 unit10