ferddle has asked for the wisdom of the Perl Monks concerning the following question:

Monks,

I have a KML file that I need to parse. I would like to do this without the help of a module. Here is an example: 
<Placemark>
<name>This is the title</name>
...
<coordinates>12,34,0</coordinates>
</Placemark>

<Placemark>
<name>This is another title</name>
</Placemark>

<Placemark>
<name>One more</name>
<coordinates>56,78,0</coordinates>
...
<coordinates>-99,-88,0</coordinates>
</Placemark>

[download]
I would like to create hashes from all occurrences of <name> and its corresponding <coordinates>. 
foreach (@kmlFile)
     {
     if (m/<name>(.*)<\/name>/)
          {
          %{$1} = (name => "<name>$1</name");
          }
     }

[download]
Great, all I need is a way to find any <coordinates> tags that occur on lines after <name>, so that each coordinate is stored in a hash with its corresponding name. One of the problems with this is that there are some <name> tags that exist without <coordinates> (center three lines in the example above).

In other words, the code need only extract the next <coordinates> that occur after a <name> -- these coordinates would only be associated with the <name> that preceeds it, all other <coordinates> would be ignored until found again after the next <name>.

These occurrences are not necessarily on consecutive lines

From the above, I would need: 
%This is the title = 
     (
     name => "<name>This is the title</name",
     coordinates => "<coordinates>12,34,0</coordinates>",
     )

%One more = 
     (
     name => "<name>One more</name>",
     coordinates => "<coordinates>56,78,0</coordinates>",
     )

[download]

If a mod is the only option, please let me know...

Thanks for any help,

-Newbs

Replies are listed 'Best First'.
Re: RegEx Riddle
by moritz (Cardinal) on May 28, 2008 at 06:44 UTC
    Why does everybody need to parse the same piece of XML? Is this some kind of homework? Or a very popular description format of some kind?

    That said, you shouldn't try to parse XML with regexes - use a decent module from CPAN instead.

[reply]
      It seems to be used by Google in Google Earth and Maps, and is referred to as KML.
[reply]
Re: RegEx Riddle
by prasadbabu (Prior) on May 28, 2008 at 05:47 UTC

    Hi ferddle,

    You can use negative look ahead regex to accomplish your job. If you have whole file in a string $kml, then

    use strict;
use warnings;
use Data::Dumper;

my $kml = do { local $/, <DATA>};

my %hash;

while ($kml =~ m/<name>((?:(?!<name>).)*)<\/name>\s*(<coordinates>(?:(
+?:(?!<coordinates>).)*)<\/coordinates>)/gs){

$hash{$1} = $2;

}

print Dumper \%hash;

output:
-------
$VAR1 = {
          'One more' => '<coordinates>56,78,0</coordinates>',
          'This is the title' => '<coordinates>12,34,0</coordinates>'
        };

    [download]

    You can learn more about positive look ahead at perlre.

    updated, added code. Thanks to ikegami for pointing out the mistake.

    Prasad

[reply]
[d/l]
      I'd take a different tack, and loop through the placemark nodes.

      I've also assumed the OP wants all coords, rather than the last one as per your example, so have dumped them in a hash of arrays... 

      my $xml = 'your xml...';
my %coords_by_name;

while ($xml =~ m{<Placemark>(.*?)</Placemark>}gs ) {
    my $placemark_snippet = $1;
    if ( $placemark_snippet =~ m{(<name>.*?</name>)}gs ) {
        my $name = $1;
        while ( $placemark_snippet =~ m{(<coordinates>.*?</coordinates
+>)}gs ) {
            push @{$coords_by_name{$name}}, $1;
        }
    }
}

use Data::Dumper;
print Dumper(\%coords_by_name);

      [download]
      I agree with the other comments though, you need a good reason to not use a proper xml parser, the above code won't be very robust, and only supports a fraction of the valid ways you could write that xml.
      ---
      my name's not Keith, and I'm not reasonable.
[reply]
[d/l]
Re: RegEx Riddle
by punch_card_don (Curate) on May 28, 2008 at 18:28 UTC
    What about some good old plain logic?

    What I read is that you want to associate the very next occurrence of coordinates, and the next occurrence only, with the last occurring name. Then: 

    $coords_found_flag = 0;
open(KMLFILE, $kml_file) or die("cannot open file : $kml_file $! ");
while ($line = <KMLFILE>) {
    if ($line =~ m/<name>(.*)<\/name>/) {
        $current_name = $1;
        $coords_found_flag = 0;
    }
    elsif ($line =~ m/<coordinates>(.*)<\/coordinates>/ && $coords_fou
+nd_flag == 0) {
        $coords{$current_name} = $1;
        $coords_found_flag = 1;
    }
}
close(KMLFILE);

    [download]



    Forget that fear of gravity,
    Get a little savagery in your life.
[reply]
[d/l]

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