xsl 1.0 muenchian sum to sum quantity field per compound key - xslt-1.0

Question

For a SAP PO xsl 1.0 mapping I need to map an 'exotic' file coming from our warehouse where I need to group/sum per order (RECH) a QTY field on a combination of a line identifier (MASTER_PO_LINE_NO) and an Itemnumber (SKU). Each line (RECL) is in a header (RECH).
INPUT:
<?xml version="1.0" encoding="UTF-8"?>
<ns0:Messages xmlns:ns0="http://sap.com/xi/XI/SplitAndMerge">
<ns0:Message1>
<MARCXML>
<RCIC>
<RECH>
<SALESID>24000</SALESID>
<RECL>
<LINE_NO>1</LINE_NO>
<QTY_EXPE>1592</QTY_EXPE>
<SKU>11207-210</SKU>
<MASTER_PO_LINE_NO>10</MASTER_PO_LINE_NO>
</RECL>
<RECL>
<LINE_NO>2</LINE_NO>
<QTY_EXPE>1000</QTY_EXPE>
<SKU>11207-210</SKU>
<MASTER_PO_LINE_NO>10</MASTER_PO_LINE_NO>
</RECL>
<RECL>
<LINE_NO>3</LINE_NO>
<QTY_EXPE>175</QTY_EXPE>
<SKU>11207-210</SKU>
<MASTER_PO_LINE_NO>20</MASTER_PO_LINE_NO>
</RECL>
</RECH>
<RECH>
<SALESID>25001</SALESID>
<RECL>
<LINE_NO>1</LINE_NO>
<QTY_EXPE>440</QTY_EXPE>
<SKU>20000-210</SKU>
<MASTER_PO_LINE_NO>10</MASTER_PO_LINE_NO>
</RECL>
</RECH>
</RCIC>
</MARCXML>
</ns0:Message1>
</ns0:Messages>
Required OUTPUT (Qty for 11207-210 = 1592 + 1000):
<?xml version="1.0" encoding="UTF-8"?>
<ns0:Messages xmlns:ns0="http://sap.com/xi/XI/SplitAndMerge">
<ns0:Message1>
<MARCXML>
<RCIC>
<RECH>
<SALESID>24000</SALESID>
<RECL>
<LINE_NO>1</LINE_NO>
<QTY_EXPE>2592</QTY_EXPE>
<SKU>11207-210</SKU>
<MASTER_PO_LINE_NO>10</MASTER_PO_LINE_NO>
</RECL>
<RECL>
<LINE_NO>3</LINE_NO>
<QTY_EXPE>175</QTY_EXPE>
<SKU>11207-210</SKU>
<MASTER_PO_LINE_NO>20</MASTER_PO_LINE_NO>
</RECL>
</RECH>
<RECH>
<SALESID>25001</SALESID>
<RECL>
<LINE_NO>1</LINE_NO>
<QTY_EXPE>440</QTY_EXPE>
<SKU>20000-210</SKU>
<MASTER_PO_LINE_NO>10</MASTER_PO_LINE_NO>
</RECL>
</RECH>
</RCIC>
</MARCXML>
</ns0:Message1>
</ns0:Messages>
There are plenty of examples about muenchian grouping but I didn't manage to solve my requirement yet. To be honest I got as far as:
<?xml version="1.0" encoding="UTF-8"?>
<ns0:Messages xmlns:ns0="http://sap.com/xi/XI/SplitAndMerge">
<ns0:Message1>
<MARCXML>
<RCIC>
<RECH>5284</RECH>
<RECH>5284</RECH>
<RECH>5284</RECH>
</RCIC>
</MARCXML>
</ns0:Message1>
</ns0:Messages>
With the following xsl:
<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:key name="kMSTR_PO_LN_SKU" match="RECL"
use="concat(MASTER_PO_LINE_NO, '#', SKU)"/>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="RECH">
<xsl:copy>
<xsl:value-of select="sum(//MARCXML/RCIC/RECH/RECL/QTY_CHECKED_IN)" />
<xsl:for-each select="/RECL[generate-id()=generate-id(key('kMSTR_PO_LN_SKU',concat(MASTER_PO_LINE_NO,'-',SKU))[1])]">
<xsl:copy>
<SKU>
<xsl:value-of select="SKU"/>
</SKU>
<Quantity>
<xsl:value-of select="sum(key('kMSTR_PO_LN_SKU',concat(MASTER_PO_LINE_NO,'-',RECL))/QTY_EXPE)"/>
</Quantity>
</xsl:copy>
</xsl:for-each>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
Hope someone can help me on my way here

Answer 1

AFAICT, this produces the required output - but having only a single example with somewhat ambiguous rules it could be a coincidence. In any case, it should provide you with a starting point.
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:strip-space elements="*"/>
<xsl:key name="k1" match="RECL" use="concat(MASTER_PO_LINE_NO, '|', SKU)"/>
<!-- identity transform -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="RECH">
<xsl:copy>
<xsl:copy-of select="SALESID"/>
<xsl:for-each select="RECL[generate-id()=generate-id(key('k1', concat(MASTER_PO_LINE_NO,'|',SKU))[1])]">
<xsl:copy>
<xsl:copy-of select="LINE_NO"/>
<QTY_EXPE>
<xsl:value-of select="sum(key('k1', concat(MASTER_PO_LINE_NO,'|',SKU))/QTY_EXPE)" />
</QTY_EXPE>
<xsl:copy-of select="SKU | MASTER_PO_LINE_NO"/>
</xsl:copy>
</xsl:for-each>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>
Added:
In order to summarize every order (RECH) separately, you must add an identifier of the order to the key:
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:strip-space elements="*"/>
<xsl:key name="k1" match="RECL" use="concat(MASTER_PO_LINE_NO, '|', SKU, '|', generate-id(..))"/>
<!-- identity transform -->
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="RECH">
<xsl:copy>
<xsl:copy-of select="SALESID"/>
<xsl:for-each select="RECL[generate-id()=generate-id(key('k1', concat(MASTER_PO_LINE_NO,'|',SKU, '|', generate-id(..)))[1])]">
<xsl:copy>
<xsl:copy-of select="LINE_NO"/>
<QTY_EXPE>
<xsl:value-of select="sum(key('k1', concat(MASTER_PO_LINE_NO,'|',SKU, '|', generate-id(..)))/QTY_EXPE)" />
</QTY_EXPE>
<xsl:copy-of select="SKU | MASTER_PO_LINE_NO"/>
</xsl:copy>
</xsl:for-each>
</xsl:copy>
</xsl:template>
</xsl:stylesheet>