Question

I have a ruby method that performs a complex data collection and places the information in an XML file. However, I need to add a post-processing step to re-sort the results based on the text value of a particular element.

I have built the loops and added information to a hash in order to allow me to do this. What I’m having difficulty figuring out is how to loop through elements. I have tried examples in the REXML and XML libraries to no avail.

My XML file is structured like this:

<?xml version="1.0"?>
<Data>
  <Apps>
    <Master>
      <VehicleType>Tractor</VehicleType>
      <Make>International</Make>
      <Sub>
        <Model>Model 1600</Model>
        <Years>2003</Years>
        <Breakout1>Green</Breakout1>
        <Part1_PartType>Seat</Part1_PartType>
        <Part1>440K3</Part1>
     </Sub>
      <Sub>
        <Model>Model 1600</Model>
        <Years>2003</Years>
        <Breakout1>Blue</Breakout1>
        <Part1_PartType>Seat</Part1_PartType>
        <Part1>ABC87S</Part1>
     </Sub>
      <Sub>
        <Model>Model 1600</Model>
        <Years>2003</Years>
        <Breakout1>Green</Breakout1>
        <Part1_PartType>Seat</Part1_PartType>
        <Part1>440K4</Part1>
     </Sub>
   </Master>
 </Apps>
</Data>

I need to re-sort those elements on “Breakout1”, I just can’t figure out how to loop through the elements.

The loop body is basically made up of simple nested conditionals where I test for the name of the element, then perform a specific action. Any help is appreciated.

Answer 1

You can use each_element to search for and loop over elements in REXML or get_elements to return an array. Both take an xpath expression to narrow down the elements. Is this what you need?:

require "rexml/document"

XML = '<Data>
  <Apps>
    <Master>
      <VehicleType>Tractor</VehicleType>
      <Make>International</Make>
      <Sub>
        <Model>Model 1600</Model>
        <Years>2003</Years>
        <Breakout1>Green</Breakout1>
        <Part1_PartType>Seat</Part1_PartType>
        <Part1>440K3</Part1>
     </Sub>
      <Sub>
        <Model>Model 1600</Model>
        <Years>2003</Years>
        <Breakout1>Blue</Breakout1>
        <Part1_PartType>Seat</Part1_PartType>
        <Part1>ABC87S</Part1>
     </Sub>
      <Sub>
        <Model>Model 1600</Model>
        <Years>2003</Years>
        <Breakout1>Green</Breakout1>
        <Part1_PartType>Seat</Part1_PartType>
        <Part1>440K4</Part1>
     </Sub>
   </Master>
 </Apps>
</Data>'

doc = REXML::Document.new XML
doc.root.each_element('//Sub') { |sub| puts sub.get_text('Breakout1') }
sorted = doc.root.get_elements('//Sub').sort { |s1, s2| s1.get_text('Breakout1') <=> s2.get_text('Breakout1') }