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1: #!/usr/bin/perl -w
2: #
3: # treemap BLOCK HASHREF
4: # treemap BLOCK ARRAYREF
5: #
6: # Works like map, for arbitrary nested data structures. Data are
7: # are modified in-place (unlike map). Returns the original reference.
8: # Hash keys are not modified.
9: #
10: # UPDATE: now handles scalar references, and trimmed an unnecessary line
11: # as suggested by dkubb (thanks!)
12: #
13: # Handles cyclical references just fine, thank you.
14: #
15: sub treemap (&$) { &_treemap }
16: sub _treemap {
17: my ($code, $node, $refs) = @_;
18: if (not my $type = ref $node) {
19: local $_ = $node;
20: $node = &$code();
21: }
22: elsif (not exists $refs->{$node}) {
23: undef $refs->{$node}; # sneaky, eh?
24: if ($type eq 'HASH') {
25: $node->{$_} = _treemap($code, $node->{$_}, $refs) for keys %$node;
26: }
27: elsif ($type eq 'ARRAY') {
28: $_ = _treemap($code, $_, $refs) for @$node;
29: }
30: elsif ($type eq 'SCALAR') {
31: $node = \_treemap($code, $$node, $refs);
32: }
33: }
34: $node;
35: }
36:
37: ####################### EXAMPLE #############################
38:
39: $data = {
40: 'nums' => [
41: 'one',
42: 'two',
43: 'three',
44: 'four',
45: [
46: 'five',
47: 'six',
48: [
49: 'seven',
50: 'eight',
51: ]]],
52: 'two' => '2',
53: 'doh' => \'blah blah',
54: 'more' => {
55: 'a' => 'vala',
56: 'b' => 'valb',
57: 'c' => 'valc',
58: 'd' => 'vald'
59: }
60: };
61:
62: use Data::Dumper;
63: print Dumper treemap { "-=\U$_=-" } $data;
64: print Dumper treemap { s/\W/./g; $_ } $data;
65: print Dumper treemap { reverse lc } $data;
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Re: treemap
by TheoPetersen (Priest) on Feb 26, 2001 at 19:39 UTC |
Nice work.I wrote something of similar structure once for examining
values in nested arrays, and found that calling the function
again for scalars was very inefficient. You can save a
good bit of time by checking for that in the code for each
ref type.
I changed the array case like so:
elsif ($type eq 'ARRAY') {
$_ = ref() ? _treemap($code, $_, $refs) : &$code() for @$node;
}
And verified the same output with fewer instructions.
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[d/l] |
Re: treemap
by japhy (Canon) on Feb 26, 2001 at 20:34 UTC |
Why: sub treemap (&$) { &_treemap }? I've seen similar things done where the called function does some preliminary initialization, etc. But this is just creating an extra stack level.
japhy --
Perl and Regex Hacker | [reply] |
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I saw it as a way of getting the public interface to be prototyped, but the private (recursive) interface to have that extra $refs parameter.
And then I was thinking there should be a way to do it with a coderef alias, but the prototype is hooked into the coderef, not the symbolname, so I stopped thinking about that. {grin}
-- Randal L. Schwartz, Perl hacker
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I'd probably just have the one entry point and call it recursively via
&treemap( $code, $$node, $refs ), where the & should disable the prototype.
-
tye
(but my friends call me "Tye")
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[d/l]
[select] |
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Re: treemap
by princepawn (Parson) on Mar 01, 2001 at 22:03 UTC |
I like this, but it would be nice if the code refs could take
advantage of context variables, such as current depth of
recursion so that different things (such as tabbing over
or enumeration) could happen at different depths of
recursion.
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Re: treemap
by princepawn (Parson) on Mar 01, 2001 at 22:28 UTC |
Something else I just thought of. There is one other type of
tree that people deal with in Perl: directory trees.
If there were someway to tie a directory tree to a nested
Perl data structure, then treemap would be roughly
equivalent to File::Find, but this time it would
require yet another set of context variables to be useful:
$File::Find::name, $File::Find::directory, and $_.
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Directory tree is an intriguing subject. It looks like an instance of the
Composite pattern - nodes are simple nodes (files) and collections (directories).
I had a go at mapping a dirtree to a tree of hashes, in How to map a directory tree to a perl hash tree and had good advice on how to improve it.
Do you think that a Perl package would be useful? What methods would you suggest? Should it Tie to the file system?
Rudif
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Re: treemap
by bsb (Priest) on Oct 01, 2003 at 03:36 UTC |
Very nice. I love it when I someone else has
done the thinking for me.
Another thing you might consider is using isa
so that the internals of blessed data structures
get traversed.
if (UNIVERSAL::isa($node,'HASH')) { ... }
| [reply]
[d/l] |
Re: treemap
by bsb (Priest) on Oct 01, 2003 at 07:55 UTC |
Monkeying around further I found that adding this
to the end of the example:
$data->{numref} = \$data->{nums}->[0];
Produces this after the first pass:
$VAR1 = {
'nums' => [
'-=ONE=-',
...],
'numref' => \'-=-=ONE=-=-',
...
The link is lost and the leaf is visited twice.
Repeating the "-=\U$_=-" line, gives
'nums' => ['-=-=ONE=-=-', ...
'numref' => \'-=-=-=ONE=-=-=-', ...
Not likely to be a problem, but worth the note.
Update:possible fix:
$refs->{ref($_) ? $_: \$_} = undef; | [reply]
[d/l]
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