XSLT union of attributes - xslt

Question

How can I transform this XML:
<data>
<entry a="2" b="3" />
<entry a="2" c="3" />
<entry b="2" c="3" />
<entry a="1" b="2" c="3" />
</data>
Into a table containing a union of all the attributes of the entrys in the header, with either the values or blanks in the rows:
<table>
<tr><th>a</th><th>b</th><th>c</th></tr>
<tr><td>2</td><td>3</td><td> </td></tr>
<tr><td>2</td><td> </td><td>3</td></tr>
<tr><td> </td><td>2</td><td>3</td></tr>
<tr><td>1</td><td>2</td><td>3</td></tr>
</table>

Answer 1

<xsl:key name="attrs" match="data/entry/#*" use="local-name(.)"/>
<xsl:variable name="unique-attr-names" select="data/entry/#*[generate-id() = generate-id(key('attrs', local-name(.))[1])]" />
<xsl:template match="data">
<table>
<tr><xsl:call-template name="unique-attrs" /></tr>
<xsl:apply-templates />
</table>
</xsl:template>
<xsl:template name="unique-attrs">
<xsl:for-each select="$unique-attr-names">
<xsl:sort data-type="text" order="ascending" />
<th><xsl:value-of select="local-name(.)"/></th>
</xsl:for-each>
</xsl:template>
<xsl:template match="entry">
<xsl:variable name="e" select="." />
<tr>
<xsl:for-each select="$unique-attr-names">
<xsl:sort data-type="text" order="ascending" />
<xsl:variable name="a" select="." />
<th><xsl:value-of select="($e/#*[local-name() = local-name($a)])[1]" /></th>
</xsl:for-each>
</tr>
</xsl:template>

Answer 2

You may also try this (based on muenchian grouping):
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" >
<xsl:output method="xml" />
<xsl:key name="kEntryAttr" match="entry/#*" use="name()" />
<xsl:template match="#*|node()">
<xsl:copy>
<xsl:apply-templates select="#*|node()"/>
</xsl:copy>
</xsl:template>
<xsl:template match="entry">
<xsl:variable name="e" select="." />
<tr>
<xsl:for-each select="//entry/#*[count(. | key('kEntryAttr', name() )[1] ) = 1]" >
<td>
<xsl:value-of select="$e/#*[name() = name(current() )]"/>
</td>
</xsl:for-each>
</tr>
</xsl:template>
<xsl:template match="*">
<table>
<tr>
<xsl:for-each select="//entry/#*[count(. | key('kEntryAttr', name() )[1] ) = 1]" >
<th>
<xsl:value-of select="name()"/>
</th>
</xsl:for-each>
</tr>
<xsl:apply-templates select="entry" />
</table>
</xsl:template>
</xsl:stylesheet>
Which will generate the following output.
<?xml version="1.0"?>
<table>
<tr>
<th>a</th>
<th>b</th>
<th>c</th>
</tr>
<tr>
<td>2</td>
<td>3</td>
<td/>
</tr>
<tr>
<td>2</td>
<td/>
<td>3</td>
</tr>
<tr>
<td/>
<td>2</td>
<td>3</td>
</tr>
<tr>
<td>1</td>
<td>2</td>
<td>3</td>
</tr>
</table>