XSLT - Merge One Header with One LineItem to One Header Multiple Line Items

Need to merge Line Ids with same Header ID under one Header

please see Below example , there are two lines with same header ID , need to merge the lines with same header id under one header. please see sample input and requested out

Input:

<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178919</headerId>
<Line>
    <LineId>112864555</LineId>
    <errorMessage>To Organization is not valid</errorMessage>
</Line>
</Header>
<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178537</headerId>
<Line>
    <LineId>112864083</LineId>
    <errorMessage>To Organization is not valid </errorMessage>
</Line>
</Header>
<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178537</headerId>
<Line>
    <LineId>112864084</LineId>
    <errorMessage>From Organization is not valid</errorMessage>
</Line>
</Header>

Requested Output

<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178919</headerId>
<Line>
    <LineId>112864555</LineId>
    <errorMessage>To Organization is not valid</errorMessage>
</Line>
</Header>
<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178537</headerId>
<Line>
    <LineId>112864083</LineId>
    <errorMessage>To Organization is not valid </errorMessage>
</Line>
<Line>
    <LineId>112864084</LineId>
    <errorMessage>From Organization is not valid</errorMessage>
</Line>
</Header>

Solution

Based on 'Adding an Element to Several Groups' from

https://www.w3.org/TR/xslt20/#grouping-examples

I used

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="2.0">
   <xsl:template match="ErrorList">
      <xsl:for-each-group select="Header" group-by="headerId">
         <header>
            <xsl:copy-of select="ackProcess"/>
            <xsl:copy-of select="headerId"/>
            <xsl:for-each select="current-group()">
               <xsl:copy-of select="Line"/>
            </xsl:for-each>
         </header>
      </xsl:for-each-group>
   </xsl:template>
</xsl:stylesheet>

<ErrorList>
<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178919</headerId>
<Line>
    <LineId>112864555</LineId>
    <errorMessage>To Organization is not valid</errorMessage>
</Line>
</Header>
<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178537</headerId>
<Line>
    <LineId>112864083</LineId>
    <errorMessage>To Organization is not valid </errorMessage>
</Line>
</Header>
<Header>
<ackProcess>Error</ackProcess>
<headerId>2005178537</headerId>
<Line>
    <LineId>112864084</LineId>
    <errorMessage>From Organization is not valid</errorMessage>
</Line>
</Header>
</ErrorList>

at https://linangdata.com/xslt-tester/ to get

<?xml version="1.0" encoding="UTF-8"?><header><ackProcess>Error</ackProcess><headerId>2005178919</headerId><Line>
    <LineId>112864555</LineId>
    <errorMessage>To Organization is not valid</errorMessage>
</Line></header><header><ackProcess>Error</ackProcess><headerId>2005178537</headerId><Line>
    <LineId>112864083</LineId>
    <errorMessage>To Organization is not valid </errorMessage>
</Line><Line>
    <LineId>112864084</LineId>
    <errorMessage>From Organization is not valid</errorMessage>
</Line></header>

as required up to formatting.