Return nodes of unique values based on 2 key parameters in XSLT1.0 - xslt-1.0

Question

Have the following input
<LIN>
<REF>
<D_127>EQ</D_127>
</S_REF>
<L_SDP>
<S_FST>
<D_127>D0317D02</D_127>
</S_FST>
</L_SDP>
<L_SDP>
<S_FST>
<D_127>D0317D03</D_127>
</S_FST>
</L_SDP>
<L_SDP>
<S_FST>
<D_127>D0317D04</D_127>
</S_FST>
</L_SDP>
</L_LIN>
<L_LIN>
<S_REF>
<D_127>1A</D_127>
</S_REF>
<L_SDP>
<S_FST>
<D_127>D0317D02</D_127>
</S_FST>
</L_SDP>
</L_LIN>
<L_LIN>
<S_REF>
<D_127>1A</D_127>
</S_REF>
<L_SDP>
<S_FST>
<D_127>D0317D02</D_127>
</S_FST>
</L_SDP>
</L_LIN>
Would now like to have the following output
<DOC>
<ITEM>
<D_127>EQ</D_127>
<D_127>D0317D02</D_127>
</ITEM>
<ITEM>
<D_127>EQ</D_127>
<D_127>D0317D03</D_127>
</ITEM>
<ITEM>
<D_127>EQ</D_127>
<D_127>D0317D04</D_127>
</ITEM>
<ITEM>
<D_127>1A</D_127>
<D_127>D0317D02</D_127>
</ITEM>
</DOC>
i want unique based on ref value and fst value.like to have items with combination of unique REF(EQ or 1A ) with S_FST(D0317D02) values. I am using XSLT 1.0 .when i use generate id i am getting some missing values...tried many combinations but couldn't get it . used for each loop for ref and fst values but couldn't get the required no of lines with combination.

Answer 1

As with most (advanced) grouping tasks in XSLT 1, declare a key, here one that concatenates the two values, then process only the first item for each group established by the key:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
version="1.0">
<xsl:output indent="yes"/>
<xsl:key name="group" match="S_FST/D_127" use="concat(., '|', ancestor::L_LIN/S_REF/D_127)"/>
<xsl:template match="ROOT">
<xsl:copy>
<xsl:apply-templates
select="//S_FST/D_127[generate-id() = generate-id(key('group', concat(., '|', ancestor::L_LIN/S_REF/D_127))[1])]"/>
</xsl:copy>
</xsl:template>
<xsl:template match="S_FST/D_127">
<ITEM>
<xsl:copy-of select="ancestor::L_LIN/S_REF/D_127"/>
<xsl:copy-of select="."/>
</ITEM>
</xsl:template>
</xsl:stylesheet>
https://xsltfiddle.liberty-development.net/bEJbVrb