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Re^3: how to construct tree from parent pointer list

by ikegami (Pope)
on Jun 30, 2009 at 13:59 UTC ( #776031=note: print w/replies, xml ) Need Help??


in reply to Re^2: how to construct tree from parent pointer list
in thread how to construct tree from parent pointer list

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?

Replies are listed 'Best First'.
Re^4: how to construct tree from parent pointer list
by bryank (Acolyte) on Jun 30, 2009 at 14:18 UTC
    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.

      The module does provide an example for output,

      The module's traverse is useless in most circumstances since it provides a flat list.

      Basically, I didn't know what to do since I couldn't find a tree object?

      Every node is a Tree object.

Re^4: how to construct tree from parent pointer list
by bryank (Acolyte) on Jun 30, 2009 at 16:00 UTC
    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..

      For example, what is '$cb'

      The first argument. It's expected to be a code reference.

      What I am trying to do is output the tree in a flattened format once the tree is built.

      Based on the code from Re: Tree path analyzer regex problem (maybe other issues)?, a reply in an older thread of yours,

      sub leaves { my $node = shift; my @children = $node->children(); if (!@children) { print(join('|', @_), "\n"); } else { for my $child (@children) { leaves($child, @_, $child->value()); } } }

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