#!/perl use strict; use warnings FATAL => qw(all); use Text::CSV_XS; use Data::Dump; my $csv_par = { binary => 1, auto_diag => 1, allow_whitespace => 1, sep_char => ';', eol => $/, quote_char => undef, }; my $csv = Text::CSV_XS->new($csv_par); my @data = @{ $csv->getline_all(*DATA) }; shift @data; # simply throw away the header. my %main; my %first_pass; for my $row ( @data ) { $first_pass{$row->[0]} = $row->[1]; $main{$row->[0]} = $row->[1]; } my %second_pass; for my $row (@data) { if ( $first_pass{$row->[1]} ) { $second_pass{$row->[0]} = $row->[1]; $main{ $row->[0] } = $main{ $row->[1] } || $row->[1]; } } my %third_pass; for my $row (@data) { if ( $second_pass{$row->[1]} ) { $third_pass{$row->[0]} = $row->[1]; $main{ $row->[0] } = $main{ $row->[1] } || $row->[1]; } } my %fourth_pass; for my $row (@data) { if ( $third_pass{$row->[1]} ) { $fourth_pass{$row->[0]} = $row->[1]; $main{ $row->[0] } = $main{ $row->[1] } || $row->[1]; } } for my $row ( @data ) { $main{$row->[1]} = "" unless exists $main{$row->[1]} or $row->[1] eq ""; } for my $num ( sort {$a <=> $b} keys %main ) { $main{$num} = $num unless length($main{$num}); print "$num => $main{$num}$/"; } # Sample chains: # 123-234-345-456-567 # 117-228-339 # 131 # 213-324-435 # 372 __DATA__ NUM;NUMPRED 567;456 456;345 345;234 234;123 339;228 228;117 131; 435;324 324;213 372;