How to copy values by matching nodes in XSLT - xslt

Question

In my XML I want to copy values into one node from another node if both nodes have matching values in some other nodes.
<XML>
<ORG>
<ITM>
<NUM>1</NUM>
<SEQ>10</SEQ>
<VAL>X</VAL>
</ITM>
<ITM>
<NUM>2</NUM>
<SEQ>20</SEQ>
<VAL>Y</VAL>
</ITM>
</ORG>
<NEW>
<ITM>
<NUM>1</NUM>
<SEQ>10</SEQ>
<VAL>QQQ</VAL>
</ITM>
</NEW>
</XML>
This works, but for large documents it might be slow, is there a better way?
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="ORG/ITM/VAL">
<xsl:variable name="NUM" select="../NUM"/>
<xsl:variable name="SEQ" select="../SEQ"/>
<VAL>
<xsl:value-of select="../../../NEW/ITM/VAL[../NUM=$NUM and ../SEQ=$SEQ]"/>
</VAL>
</xsl:template>
</xsl:stylesheet>
The result has the value "QQQ" in the ORG/ITM/VAL node since ORG/ITM/NUM and ORD/ITM/SEQ match with NEW/ITM/NUM and NEW/ITM/SEQ
<?xml version="1.0"?>
<XML>
<ORG>
<ITM>
<NUM>1</NUM>
<SEQ>10</SEQ>
<VAL>QQQ</VAL>
</ITM>
<ITM>
<NUM>2</NUM>
<SEQ>20</SEQ>
<VAL/>
</ITM>
</ORG>
<NEW>
<ITM>
<NUM>1</NUM>
<SEQ>10</SEQ>
<VAL>QQQ</VAL>
</ITM>
</NEW>
</XML>

Answer 1

The preferred method to lookup values is to define a key and use it. In the given example, this could be:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:key name="new-item" match="NEW/ITM" use="concat(NUM, '|', SEQ)" />
<!-- identity transform -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="ORG/ITM/VAL">
<xsl:copy>
<xsl:value-of select="key('new-item', concat(../NUM, '|', ../SEQ))/VAL"/>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>

Answer 2

using 1 variable is more faster.
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="ORG/ITM/VAL">
<xsl:variable name="NUMSEQ" select="concat(string(../NUM), string(../SEQ))"/>
<VAL>
<xsl:value-of select="../../../NEW/ITM/VAL[concat(string(../NUM), string(../SEQ))=$NUMSEQ]"/>
</VAL>
</xsl:template>
</xsl:stylesheet>