Question

For an XML file that has the following structure

 <?xml version="1.0" encoding="UTF-8">
 <farm xmlns:my="mynamespace.com" >
   <pen>
    <sheep> 3 </sheep>
    <cow> 3</cow>
    <pig> 2</pig>
    <chicken> 5</chicken>
   </pen>
  <pen>
    <sheep> 12 </sheep>
    <cow> 1</cow>
    <pig> 2</pig>
    <chicken> 4</chicken>
   </pen>
  <pen>
    <sheep> 4 </sheep>
    <cow> 4</cow>
    <pig> 1</pig>
    <chicken> 2</chicken>
   </pen>
 </farm>

I have an xsl style sheet that loops through each pen node(for-each), generates an id for each animal type, i.e. sheep,cow,pig and chicken and counts the total. Generating a table as below

ANIMAL   | VALUE
-----------------
pig      |  5
cow      |  8
sheep    | 19
chickens | 11

Now I would like to have this resultset sorted, by the value column
Is it possible to do the equivalent of a subquery using XSL?

Answer 1

This XSLT 1.0 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:key name="kAnimalByName" match="pen/*" use="name()"/>

 <xsl:template match="/*">
     <table border="1">
      <thead>
          <tr>
           <td>Animal</td>
           <td>Total</td>
          </tr>
      </thead>
      <tbody>
       <xsl:apply-templates select=
        "/*/pen/*
           [generate-id()
           =
            generate-id(key('kAnimalByName', name())[1])
            ]">
         <xsl:sort select="sum(/*/pen/*[name() = name(current())])"
                   data-type="number"/>
       </xsl:apply-templates>
      </tbody>
     </table>
 </xsl:template>

 <xsl:template match="pen/*">
  <tr>
   <td><xsl:value-of select="name()"/></td>
   <td>
     <xsl:value-of select="sum(/*/pen/*[name() = name(current())])"/>
   </td>
  </tr>
 </xsl:template>
</xsl:stylesheet>

when applied on the provided XML document:

<farm xmlns:my="mynamespace.com" >
    <pen>
        <sheep> 3 </sheep>
        <cow> 3</cow>
        <pig> 2</pig>
        <chicken> 5</chicken>
    </pen>
    <pen>
        <sheep> 12 </sheep>
        <cow> 1</cow>
        <pig> 2</pig>
        <chicken> 4</chicken>
    </pen>
    <pen>
        <sheep> 4 </sheep>
        <cow> 4</cow>
        <pig> 1</pig>
        <chicken> 2</chicken>
    </pen>
</farm>

produces the wanted, correct result:

<table border="1">
   <thead>
      <tr>
         <td>Animal</td>
         <td>Total</td>
      </tr>
   </thead>
   <tbody>
      <tr>
         <td>pig</td>
         <td>5</td>
      </tr>
      <tr>
         <td>cow</td>
         <td>8</td>
      </tr>
      <tr>
         <td>chicken</td>
         <td>11</td>
      </tr>
      <tr>
         <td>sheep</td>
         <td>19</td>
      </tr>
   </tbody>
</table>

Explanation: Proper use of the Muenchian method for grouping.