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    copied!<p><strong>Here is a solution using Muenchian grouping</strong>:</p> <pre><code>&lt;xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"&gt; &lt;xsl:output omit-xml-declaration="yes" indent="yes"/&gt; &lt;xsl:key name="kBookByNums" match="Book" use="number(current_inventory)"/&gt; &lt;xsl:template match="/*"&gt; &lt;xsl:for-each select= "Book [generate-id() = generate-id(key('kBookByNums', number(current_inventory) )[1] ) ] "&gt; &lt;xsl:sort select="current_inventory" data-type="number" order="descending"/&gt; &lt;xsl:if test="position()=1"&gt; &lt;xsl:copy-of select= "key('kBookByNums', number(current_inventory) )"/&gt; &lt;/xsl:if&gt; &lt;/xsl:for-each&gt; &lt;/xsl:template&gt; &lt;/xsl:stylesheet&gt; </code></pre> <p><strong>When this transformation is applied on the provided XML document, the correct result is produced</strong>:</p> <pre><code>&lt;Book&gt; &lt;sku&gt;12345&lt;/sku&gt; &lt;title&gt;Beauty Secrets&lt;/title&gt; &lt;condition&gt;New&lt;/condition&gt; &lt;current_inventory&gt;20&lt;/current_inventory&gt; &lt;price&gt;99.99&lt;/price&gt; &lt;/Book&gt; &lt;Book&gt; &lt;sku&gt;54321&lt;/sku&gt; &lt;title&gt;Picturescapes&lt;/title&gt; &lt;current_inventory&gt;20&lt;/current_inventory&gt; &lt;condition&gt;New&lt;/condition&gt; &lt;price&gt;50.00&lt;/price&gt; &lt;/Book&gt; </code></pre> <p><strong>Update</strong>:</p> <p>It may seem that this xsl-key's solution "plays its 'efficiency card' for large input documents only (i.e. thousands of books). " as someone put it. In fact, such a statement is quite imprecise.</p> <p><strong>The improvement in eficiency can be large even when there are not so many items</strong>, <em>if the number of different values is very small, compared to the total number of values</em>. So, even for fairly small sets of items (one-two hundred), there is significant effect if the number of different values is not more than 10-20 -- something that happens in a lot of real-world cases.</p> <p><strong>What matters is the small ratio of the number of different values to the total size</strong>.</p>
 

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