chunk – Read a large (XML) file a chunk at a time

I’ve recently had to parse some pretty large XML documents, and needed a method to read one element at a time.

Here’s a fairly simple solution in PHP and Ruby form (hopefully a Python one coming soon…).

If you have the following file (complex-test.xml):



  
    Title 1
    It's name goes here
    
      
      
      
      
    
    
  
  
  
    
    
  
  
  

And wanted to return the <Object/>s

PHP:

require_once('class.chunk.php');

$file = new Chunk('complex-test.xml', array('element' => 'Object'));

while ($xml = $file->read()) {
  $obj = simplexml_load_string($xml);
  // do some parsing, insert to DB whatever
}

Ruby:

require 'chunk.rb'

file = Chunk.new('complex-test.xml', { 'element' => 'Object' })

while xml = file.read
  doc = REXML::Document.new(xml)
  // do some parsing, blah...
end

It (probably) doesn’t work with nested XML elements, but the use I had for it didn’t require that it did.

You can get the PHP version here, and the Ruby one here.

Update: The class was accepted onto PHP Classes as a notable package! 04/08/2009.

6 Replies to “chunk – Read a large (XML) file a chunk at a time”

  1. This code helped me parse some very large files quickly, however when I try to create more than one chunk instance in a script, it will error out. I am not quite sure why this is happening. I receive the following exception when I try to read the second XML file in:

    ./chunk.rb:223:in `+': can't convert nil into String (TypeError)
    	from ./chunk.rb:223:in `read'
    

    I am calling Chunk.new again, so I am not sure why a second execution would cause this behavior. If I execute each import separately, everything works. Any help is greatly appreciated.

    1. Hi there Ben,

      I’ll certainly have a play with it and see if it’s something I can resolve quickly, not sure why it would have any impact though…

      Thanks for pointing this out!

      Dom

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