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map <IF> to hash with replacement

by vit (Pilgrim)
on Feb 04, 2010 at 23:37 UTC ( #821475=perlquestion: print w/ replies, xml ) Need Help??
vit has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,
I have an XML file which I want to convert to hash removing tags. It is not a problem, but I want to do it nice with one map {}
This works
my %hash = map { lc($_), 1 } <IF>;
but I need something like that
%hash = map { lc($_), 1; s/<tag>//; s/<\/tag>// } <IF>;
which does not work.

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Re: map <IF> to hash with replacement
by almut (Canon) on Feb 04, 2010 at 23:52 UTC
    %hash = map { $_=lc($_); s/<tag>//; s/<\/tag>//; $_ => 1 } <IF>;
      So in map we go from left to right ?

        map 'returns' a result for each element processed. The result is the last value of the last statement in the map block and may be a list. Consider:

        #!/usr/bin/perl use strict; use warnings; my @lines = qw(<tag>A</tag> <TAG>B</TAG> <tag>C</tag>); for my $expr ( 'lc', 'lc($_), 1', '$_=lc($_); s/<tag>//; s/<\/tag>//; $_ => 2' ) { my @values = eval "map {$expr} \@lines"; print join("\n ", "map {$expr} =>", @values), "\n"; }

        Prints:

        map {lc} => <tag>a</tag> <tag>b</tag> <tag>c</tag> map {lc($_), 1} => <tag>a</tag> 1 <tag>b</tag> 1 <tag>c</tag> 1 map {$_=lc($_); s/<tag>//; s/<\/tag>//; $_ => 2} => a 2 b 2 c 2

        That result can be a list (as shown by almut


        True laziness is hard work

        Yes.  Just like you normally go from top to bottom when the statements are written on separate lines:

        { $_=lc($_); s/<tag>//; s/<\/tag>//; $_ => 1 }

        Statements are always executed from the earliest in the file to the latest in the file (unless overridden by loops, etc, of course). The statements in a map block are no exception.

        Yes, just like in a program we go from top to bottom.

Re: map <IF> to hash with replacement
by crashtest (Curate) on Feb 05, 2010 at 01:49 UTC

    Your immediate problem seems to be solved, but based on your question, I am guessing you are doing some sort of XML processing. If you are, I'd suggest you skip re-inventing any wheels and consider the resources already available.

    The main XML parsing module on CPAN is XML::Parser. A handier interface to it is provided by XML::Simple.

    PerlMonks has a tutorial on XML::Parser, although it's almost ten years old.

    Edit: As I wrote this, in the back of my mind I was hoping that another monk would help out in case my recommendations were out of date. Your Mother came through - thanks!

      I understand this is well intentioned but I think it's bad advice. XML::Twig, XML::Rules, and XML::LibXML are probably all to be preferred over XML::Parser; I'd argue the libxml wrapper is definitely a better choice. And XML::Simple is anything but; it's a maze of special cases and their mapping parameters. It can be a very useful module but I wouldn't recommend it without knowing the problem and input at hand.

        I would use XML::Simple. It's dead easy to bring XML in as Perl structures.
        use XML::Simple qw{XMLin}; print keys %{XMLin("<root><x>1</x><y>2</y></root>")};
        This prints "xy".

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