2009-09-30-splitting-xml-well-with-xslt-2.html

---
layout: post
title: "Splitting XML Well with XSLT 2"
permalink: splitting-xml-well-with-xslt-2.html
categories: [xml, xslt, xslt2, split]
---

<p>I recently had the need to split up a result set from a <a
href="http://lucene.apache.org/solr/">Solr</a> query into a collection
of smaller groups of <code>add</code> requests for POSTing into a
different core.
There are some ways to make the split work with text processing tools
(<code>split</code> and friends), but it's always an open question
whether an ad hoc approach will trip over some markup &#8212; it's
just better to use XML tooling.  By no coincidence (based on features missing from 
<a href="http://www.w3.org/TR/xslt"></a>), <a href="http://www.w3.org/TR/xslt20/">XSLT&#160;2</a> makes it
easy to do the right thing.</p>

<p>First up is grouping in chunks of 2000 records:</p>

<pre class="code">&lt;xsl:for-each-group select="/response/result/doc"
                    group-by="round(position() div 2000)">
...
&lt;/xsl:for-each-group></pre>

<p>Outputting each hunk to a file named for the index of the
group is also a one-liner:</p>

<pre class="code">&lt;xsl:result-document href="{current-grouping-key()}_out.xml">
  &lt;add>
    &lt;xsl:for-each select="current-group()">
      &lt;doc>
        &lt;xsl:apply-templates />
      &lt;/doc>
    &lt;/xsl:for-each>
  &lt;/add>
&lt;/xsl:result-document></pre>

<p>And that's it.  The only trick is choosing an XSLT&#160; processor,
and the superlative <a
href="http://saxon.sourceforge.net/">Saxon</a> (from <a
href="http://www.saxonica.com/">Saxonica</a>) is my default choice.</p>