<root>
	<record>
		<key>1</key>
		<movie>Leon</movie>
	</record>
	<record>
		<key>1</key>
		<movie>Godfather</movie>
	</record>
	<record>
		<key>2</key>
		<movie>Hangover</movie>
	</record>
</root> 

<?xml version="1.0" ?>
<xsl:stylesheet version="1.0" 
 xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:key name="movies-by-key" match="record" use="key" />
<xsl:template match="root">
<root> 
	<xsl:for-each select="record[count(. | key('movies-by-key', key)[1]) = 1]">
<record>
<key>
<xsl:value-of select="key" />
</key>
<movies> 
		<xsl:for-each select="key('movies-by-key', key)">
<movie>
			<xsl:value-of select="movie" /> 
</movie>
		</xsl:for-each>
</movies>
</record> 
	</xsl:for-each>
</root> 
</xsl:template>
</xsl:stylesheet>