Beefy Boxes and Bandwidth Generously Provided by pair Networks
The stupid question is the question not asked
 
PerlMonks  

Re: how to construct tree from parent pointer list

by ikegami (Pope)
on Mar 21, 2006 at 22:40 UTC ( #538333=note: print w/replies, xml ) Need Help??


in reply to how to construct tree from parent pointer list

Getting you started with the previously mentioned Tree module:

use Tree (); my %nodes; while (<>) { my ($child, $parent) = split /:/; my $parent_node = $nodes{$parent} ||= Tree->new($parent); my $child_node = $nodes{$child} ||= Tree->new($child); $parent_node->add_child($child_node); } my @roots = grep { $_->is_root } values %nodes; die("Invalid data: No roots\n") unless @roots; foreach (@roots) { ... }
If you are only expecting one root, replace the bottom loop with:
die("Invalid data: Multiple roots\n") if @roots > 1; my $root = $roots[0]; ...

I didn't check for circular dependancies.

Replies are listed 'Best First'.
Re^2: how to construct tree from parent pointer list
by bryank (Acolyte) on Jun 30, 2009 at 13:30 UTC
    Hi,

    How do you output the tree? I tried using the various Tree methods with the keys of the hash, but without success.

      Like any other tree.
      sub visit_preorder { my ($cb, node, $depth) = @_; $depth ||= 0; $cb->($node, $depth); visit_preorder($cb, $_, $depth+1) for $node->children(); } sub visit_postorder { my ($cb, $node, $depth) = @_; $depth ||= 0; visit_postorder($cb, $_, $depth+1) for $node->children(); $cb->($node, $depth); } visit_preorder(sub { my ($node, $depth) = @_; ... }, $root);

      It's odd that the module doesn't provide this for you.

      What's wrong with the solutions we've already customised for you?

        Thanks. The module does provide an example for output, but I couldn't figure out how to implement it in the example shown here. For example, here is what the module gives:

        my @nodes = $tree->traverse( $tree->PRE_ORDER );
        The example I was working off of:

        use Tree (); my %nodes; while (<>) { my ($child, $parent) = split /:/; my $parent_node = $nodes{$parent} ||= Tree->new($parent); my $child_node = $nodes{$child} ||= Tree->new($child); $parent_node->add_child($child_node); } my @roots = grep { $_->is_root } values %nodes; die("Invalid data: Multiple roots\n") if @roots > 1; my $root = $roots[0];

        Basically, I didn't know what to do since I couldn't find a tree object? I'm sure I am missing all sorts of obvious signs in the code -- I am just too much of a newby to fully understand it. Sorry.

        Hi, Can you explain what the pieces of this does

        sub visit_preorder { my ($cb, node, $depth) = @_; $depth ||= 0; $cb->($node, $depth); visit_preorder($cb, $_, $depth+1) for $node->children(); }

        For example, what is '$cb' ? What I am trying to do is output the tree in a flattened format once the tree is built. Something like : Fruit|Apple|Granny Smith.. Fruit being the parent of Apple, Apple being the parent of Granny Smith..

Log In?
Username:
Password:

What's my password?
Create A New User
Node Status?
node history
Node Type: note [id://538333]
help
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others examining the Monastery: (5)
As of 2020-11-23 22:29 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?

    No recent polls found

    Notices?