On Fri, Jun 5, 2009 at 09:19, William <[email protected]> wrote:
>
> I have been trying for hours, to make this data structure into hash, I need
> help. Thanks.
>
> $str =
> "
> (dr1
> <predicate>foo
> <1>(dr2 <predicate>bar)
> <2>a
> )
> ";
>
> $hash = {
> "dr1" => {
> "<1>" => {"dr2" => {"predicate"=> "bar"}},
> "<2>" => "a"
> }
> };
snip
> What could be the regular expression and algorithm to make the resulting hash
> ?
snip
This isn't really a job for a regex. Note that you have a recursive
structure (parentheses can contain parentheses). When you have a
recursive structure you are moving out of the realm of regexes and
into the realm of parsers. A good general purpose parser is
Parse::RecDescent[1], and you should learn to use it, but your example
is simple enough that we don't need it. We can tokenize the stream
fairly easily by splitting on '(', ')', '<', '>', and whitespace, then
throwing out the whitespace characters[2]. Once we have the tokens we
deal with each () group recursively:
#!/usr/bin/perl
use strict;
use warnings;
my $s = "
(dr1
<predicate>foo
<1>(dr2 <predicate>bar)
<2>a
)
";
my @tokens = grep { /\S/ } split /([()<>\s])/, $s;
my $hash = recurse(\...@tokens);
use Data::Dumper;
print Dumper $hash;
sub recurse {
my $tokens = shift;
my $paren = shift @$tokens;
my $key = shift @$tokens;
die "invalid structure" unless $paren eq '(';
my %hash;
while (@$tokens) {
my $start = shift @$tokens;
my $subkey = shift @$tokens;
my $end = shift @$tokens;
die "invalid structure" unless $start eq '<' and $end eq '>';
if ($tokens->[0] eq '(') {
$hash{$key}{$subkey} = recurse($tokens);
} else {
$hash{$key}{$subkey} = shift @$tokens;
}
if ($tokens->[0] eq ')') {
shift @$tokens;
return \%hash;
}
}
die "invalid structure";
}
1. http://search.cpan.org/dist/Parse-RecDescent/lib/Parse/RecDescent.pm
2. if whitespace is allowed between '<' and '>', this will need to
change slightly
--
Chas. Owens
wonkden.net
The most important skill a programmer can have is the ability to read.
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