xslt Format data in a table some columns are blank - xslt

Question

With XSLT 1.0, how can I change the following:
<root>
<element id="1" Team="Rangers" Season="2011" Points="12" />
<element id="2" Team="Rangers" Season="2012" Points="5" />
<element id="3" Team="Rangers" Season="2013" Points="3" />
<element id="4" Team="Astros" Season="2011" Points="12" />
<element id="5" Team="Astros" Season="2013" Points="2" />
</root>
Into:
<table>
<tr><td>Team</td>
<td>2011</td>
<td>2012</td>
<td>2013</td>
<td>Total</td></tr>
<tr><td>Rangers</td>
<td>12</td>
<td>5</td>
<td>3</td>
<td>20</td></tr>
<tr><td>Astros</td>
<td>12</td>
<td>0</td>
<td>2</td>
<td>14</td></tr>
</table>
The heading can be generated manually as it is static, but I am unsure how to handle null data.
Any help would be greatly appreciated!

Answer 1

<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output indent="yes"/>
<xsl:key name="T" match="element" use="#Team"/>
<xsl:key name="S" match="element" use="#Season"/>
<xsl:template match="root">
<xsl:variable name="years" select="element[generate-id()=generate-id(key('S',#Season)[1])]"/>
<table>
<tbody>
<tr>
<td>Team</td>
<xsl:for-each select="$years">
<xsl:sort select="#Season"/>
<td><xsl:value-of select="#Season"/></td>
</xsl:for-each>
<td>Total</td>
</tr>
<xsl:for-each select="element[generate-id()=generate-id(key('T',#Team)[1])]">
<tr>
<xsl:variable name="thisteam" select="key('T',#Team)"/>
<xsl:for-each select="$years">
<xsl:sort select="#Season"/>
<td>
<xsl:choose>
<xsl:when test="$thisteam[#Season=current()/#Season]">
<xsl:value-of select="$thisteam[#Season=current()/#Season]/#Points"/>
</xsl:when>
<xsl:otherwise>
<xsl:value-of select="0"/>
</xsl:otherwise>
</xsl:choose>
</td>
</xsl:for-each>
<td><xsl:value-of select="sum($thisteam/#Points)"/></td>
</tr>
</xsl:for-each>
</tbody>
</table>
</xsl:template>
</xsl:stylesheet>
Produces
<?xml version="1.0" encoding="utf-8"?>
<table>
<tbody>
<tr>
<td>Team</td>
<td>2011</td>
<td>2012</td>
<td>2013</td>
<td>Total</td>
</tr>
<tr>
<td>12</td>
<td>5</td>
<td>3</td>
<td>20</td>
</tr>
<tr>
<td>12</td>
<td>0</td>
<td>2</td>
<td>14</td>
</tr>
</tbody>
</table>