Combining two nodesets in XSL - xslt

Question

I have the following XML:
<root>
<row>
<elem>Timestamp</elem>
<elem>ERB.CHW.BTU_CV</elem>
<elem>ERB.CHW.BTU1_CV</elem>
<elem>ERB.HW.BTU_CV</elem>
<elem>ERB.HW.BTU1_CV</elem>
<elem>ERB.KW.DEMAND_CV</elem>
<elem>ERB.KWH.MT_CV</elem>
<elem></elem>
</row>
<row>
<elem>2011/09/30 11:21:13.9062</elem>
<elem>2.307609E+09</elem>
<elem>1880067</elem>
<elem>1.068635E+08</elem>
<elem>1340.386</elem>
<elem>448.8</elem>
<elem>1427723</elem>
<elem></elem>
</row>
</root>
I want to alter it such that the first <row> defines new elements (via <elem>) and each non-empty <elem> that follows provides values - such as:
<root>
<row>
<Timestamp>2011/09/30 11:21:13.9062</Timestamp>
<ERB.CHW.BTU_CV>2.307609E+09</ERB.CHW.BTU_CV>
<ERB.CHW.BTU1_CV>1880067</ERB.CHW.BTU1_CV>
<ERB.HW.BTU_CV>1.068635E+08</ERB.HW.BTU_CV>
<ERB.HW.BTU1_CV>1340.386</ERB.HW.BTU1_CV>
<ERB.KW.DEMAND_CV>448.8</ERB.KW.DEMAND_CV>
<ERB.KWH.MT_CV>1427723</ERB.KWH.MT_CV>
</row>
</root>
Two things to note:
Notice how blank <elem> elements are removed from the source structure.
This should work for any number of <row> nodesets.
I feel like this should be simple, but I'm struggling to even know where to begin. Help?
EDIT: RE: #2 above, I am not looking to duplicate the initial <row> nodeset (which is used to define the new elements). Rather, the solution should work for any <row> nodeset that contains data points (i.e., if the second <row> nodeset was duplicated 5 times in a row).

Answer 1

This transformation:
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:variable name="vElems" select=
"/*/row[1]/elem[normalize-space()]"/>
<xsl:template match="/*">
<root>
<xsl:apply-templates select="row[position() >1]"/>
</root>
</xsl:template>
<xsl:template match="row">
<row>
<xsl:apply-templates select="$vElems">
<xsl:with-param name="pValues"
select="elem"/>
</xsl:apply-templates>
</row>
</xsl:template>
<xsl:template match="elem">
<xsl:param name="pValues"/>
<xsl:variable name="vPos" select="position()"/>
<xsl:element name="{.}">
<xsl:value-of select="$pValues[$vPos]"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
when applied on the following XML document (the provided plus one more data row):
<root>
<row>
<elem>Timestamp</elem>
<elem>ERB.CHW.BTU_CV</elem>
<elem>ERB.CHW.BTU1_CV</elem>
<elem>ERB.HW.BTU_CV</elem>
<elem>ERB.HW.BTU1_CV</elem>
<elem>ERB.KW.DEMAND_CV</elem>
<elem>ERB.KWH.MT_CV</elem>
<elem></elem>
</row>
<row>
<elem>2011/09/30 11:21:13.9062</elem>
<elem>2.307609E+09</elem>
<elem>1880067</elem>
<elem>1.068635E+08</elem>
<elem>1340.386</elem>
<elem>448.8</elem>
<elem>1427723</elem>
<elem></elem>
</row>
<row>
<elem>2011/09/31 11:22:33.9063</elem>
<elem>3.418609E+10</elem>
<elem>1991073</elem>
<elem>1.068635E+08</elem>
<elem>1340.386</elem>
<elem>452.5</elem>
<elem>169578</elem>
<elem></elem>
</row>
</root>
produces the wanted, correct result:
<root>
<row>
<Timestamp>2011/09/30 11:21:13.9062</Timestamp>
<ERB.CHW.BTU_CV>2.307609E+09</ERB.CHW.BTU_CV>
<ERB.CHW.BTU1_CV>1880067</ERB.CHW.BTU1_CV>
<ERB.HW.BTU_CV>1.068635E+08</ERB.HW.BTU_CV>
<ERB.HW.BTU1_CV>1340.386</ERB.HW.BTU1_CV>
<ERB.KW.DEMAND_CV>448.8</ERB.KW.DEMAND_CV>
<ERB.KWH.MT_CV>1427723</ERB.KWH.MT_CV>
</row>
<row>
<Timestamp>2011/09/31 11:22:33.9063</Timestamp>
<ERB.CHW.BTU_CV>3.418609E+10</ERB.CHW.BTU_CV>
<ERB.CHW.BTU1_CV>1991073</ERB.CHW.BTU1_CV>
<ERB.HW.BTU_CV>1.068635E+08</ERB.HW.BTU_CV>
<ERB.HW.BTU1_CV>1340.386</ERB.HW.BTU1_CV>
<ERB.KW.DEMAND_CV>452.5</ERB.KW.DEMAND_CV>
<ERB.KWH.MT_CV>169578</ERB.KWH.MT_CV>
</row>
</root>

Answer 2

The following stylesheet produces the requested result:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" omit-xml-declaration="yes" indent="yes"/>
<xsl:strip-space elements="*"/>
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<!-- ignore even-numbered rows -->
<xsl:template match="row[position() mod 2 = 0]"/>
<!-- non-empty elem nodes of odd-numbered rows -->
<xsl:template match="elem[normalize-space()]">
<xsl:variable name="pos" select="position()"/>
<xsl:element name="{text()}">
<xsl:value-of select="../following-sibling::row[1]/elem[$pos]"/>
</xsl:element>
</xsl:template>
<xsl:template match="elem"/>
</xsl:stylesheet>
Explanation:
The Identity Transform is used to copy most nodes through unchanged
All even-numbered rows are initially skipped
When processing the (non-empty) elem elements of each odd-numbered row, we grab the value of the elem at the same position in the row's following sibling