From: Robert Klemme <bob.news@...>
Date: 2005-06-24T17:00:38+09:00
Subject: Re: REXML Optimization

Bucco wrote:
> So, I'm reading this document on XML and using XML as a database.  Of
> course the author uses this cryptic perl script to parse the xml file:
>
> #!/usr/bin/perl
> use XML::LibXML;
> my $parser = new XML::LibXML;
> my $doc = $parser->parse_file( shift @ARGV );
> my $balance = $doc->findvalue( '/checkbook/@balance-start' );
> foreach my $record ( $doc->findnodes( '//debit' )) {
>     $balance -= $record->findvalue( 'amount' );
> }
> foreach my $record ( $doc->findnodes( '//deposit' )) {
>     $balance += $record->findvalue( 'amount' );
> }
> print "Current balance: $balance\n";
>
> So, since I was trying to figure out how to use xml as a database and
> how to use REXML I gave the script a whack and tried to write a ruby
> script to do the same thing.  Below is a sample of the xml file and
> the ruby script:
>
> <?xml version="1.0"?>
> <checkbook balanceStart="2460.62">
> <title>expenses: january 2002</title>
>
>   <debit category="clothes">
>     <amount>31.19</amount>
>     <date><year>2002</year><month>1</month><day>3</day></date>
>     <payto>Walking Store</payto>
>     <description>shoes</description>
>   </debit>
>
>   <deposit category="salary">
>     <amount>1549.58</amount>
>     <date><year>2002</year><month>1</month><day>7</day></date>
>     <payor>Bob's Bolts</payor>
>   </deposit>
> </checkbook>
>
>
> #!/usr/bin/ruby -w
> require 'rexml/document'
>
> # Read in XML doc
> doc = REXML::Document.new(File.open('cb.xml'))
> # Future version need to have entry from command line
>
> # Find the balance and assign to float variabl 'balance'
> balance = doc.root.attributes['balanceStart'].to_f
>
> # Calculate debits and balance
> doc.elements.each("//debit/amount") {|o| balance -= o.text.to_f}
> # Calculate deposits and balance
> doc.elements.each("//deposit/amount") {|i| balance += i.text.to_f}
>
> #Display final balance:
> puts balance
>
> Of course I was able to complete the same task as teh perl script in
> ruby with less code. (Not to mention easier to read code)
>
> Just to help me complete the learning process, I wish to pose the
> question to the group: Is there a better way to do this, and is there
> more optimization I can do to my code?

You could get rid of one traversal by iterating all "amounts" and do the
calculation based on the parent element's type.

Kind regards

    robert