RegEx Riddle

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

Comment on RegEx Riddle Select or Download Code

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]
Re^2: RegEx Riddle by pc88mxer (Vicar) on May 28, 2008 at 15:13 UTC
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]
Re^2: RegEx Riddle by reasonablekeith (Deacon) on May 28, 2008 at 10:12 UTC
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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