For the unimaginative ones: The last input line ought to end in name5.

A rather simple solution would use more than one hash (or array). Actually, both structures are fine. If your biggest id is much larger than the number of names then hashes might be more effective. The following isn't optimized because it unravels the ancestry several times - if performance is an issue than this could be avoided (with a bit of recursion).

use strict;
use warnings;

my %parent_id  = ();
my %id_to_name = ();

# Building the tree
while (my $line = <DATA>) {
    chomp $line;
    my ($id,$parent_id,$name) = split /,/, $line;
    $parent_id{$id}    = $parent_id;
    $id_to_name{$id}   = $name;
}

# Dumping the tree
my %name_to_id = reverse %id_to_name;
for my $name (sort keys %name_to_id) {
    my $id        = $name_to_id{$name};
    my $parent_id = $parent_id{$id};
    my @ancestors = ($name);

    while (my $name = $id_to_name{$parent_id}) {
        push @ancestors,$name;
        $parent_id = $parent_id{$parent_id};
    }

    print join(',',@ancestors),"\n"; 
}

__DATA__
15,10,name3
10,#,name1
12,10,name2
5,12,name4
8,5,name5

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In reply to Re: Reorganizing the content of a file by haj
in thread Reorganizing the content of a file by ovedpo15

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