The tree I am constructing is based on code references calling the parents subs for its parents and relations: 

use strict;
use warnings;

my %data;
while(<DATA>){
  my( $child, $parent, $relation ) = split /,\s*/;
  $data{$child} = { parent => sub { $child.(exists $data{$parent}?'<-'
+.$data{$parent}{parent}->():"<-$parent") }, 
                    relation => sub { (exists $data{$parent}?$data{$pa
+rent}{relation}->().'.':'' ).$relation } };
}

print $_->{parent}->()." = ".$_->{relation}->()."\n" for values %data;

__DATA__
M10,    Q,    P,
M143,    M10,    P,
M406,    M143,    PL,
M407,    M143,    PL,
M420,    M143,    E,
M421,    M143,    E,

[download]

In reply to Re: constructing a tree from csv file by hdb
in thread constructing a tree from csv file by zing

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.