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xmlxsltxslt-1.0xslt-grouping

Sort groups by arregate element property in xslt

I'm transforming some xml using xslt (version 1.0, using MSXSL).

Say my xml data looks like this:

<table>
 <record><name>A</name><value>a</value><size>10</size></record>
 <record><name>A</name><value>b</value><size>35</size></record>
 <record><name>A</name><value>c</value><size>60</size></record>
 <record><name>B</name><value>x</value><size>15</size></record>
 <record><name>B</name><value>y</value><size>90</size></record>
 <record><name>B</name><value>z</value><size>20</size></record>
 ...
</table>

My goal is:

  1. to group the records by <name>
  2. per group, determine the maximum <size>, say maxsize
  3. sort the groups by their maxsize (descending)
  4. per group, list the records (in original order)

So the result could be:

<table>
 <group>B<maxsize>90</maxsize>
  <record><value>x</value><size>15</size>
  <record><value>y</value><size>90</size>
  <record><value>z</value><size>20</size>
 </group>
 <group>A<maxsize>60</maxsize>
  <record><value>a</value><size>10</size>
  <record><value>a</value><size>35</size>
  <record><value>a</value><size>60</size>
 </group>
</table>

Now steps 1, 2 and 4, I can do that. But... how can I order the groups by their maximum size?

I tried building a new node set in a variable, containing the groups. I can build such a set but I can only access it as a string.

Should be possible, right?

Solution

  • Here you go:

    <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
    <xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>
  <xsl:key name="kRecord" match="record" use="name"/>

    <xsl:template match="@* | node()">
        <xsl:copy>
            <xsl:apply-templates select="@* | node()"/>
        </xsl:copy>
    </xsl:template>

  <xsl:template match="/*">
    <xsl:copy>
      <xsl:apply-templates
        select="record[generate-id() = 
                       generate-id(key('kRecord', name)[1])]" 
        mode="group">
        <xsl:sort select="key('kRecord', name)/size
                              [not(. &lt; key('kRecord', ../name)/size)]" 
                  data-type="number"
                  order="descending" />
      </xsl:apply-templates>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="record" mode="group">
    <xsl:variable name="members" select="key('kRecord', name)" />
    <group>
      <xsl:value-of select="name" />
      <maxsize>
        <xsl:value-of select="$members/size[not(. &lt; $members/size)]"/>
      </maxsize>
      <xsl:apply-templates select="$members" />
    </group>
  </xsl:template>

  <xsl:template match="record/name" />
</xsl:stylesheet>

    When run on your sample input, the result is:

    <table>
  <group>
    B<maxsize>90</maxsize><record>
      <value>x</value>
      <size>15</size>
    </record><record>
      <value>y</value>
      <size>90</size>
    </record><record>
      <value>z</value>
      <size>20</size>
    </record>
  </group>
  <group>
    A<maxsize>60</maxsize><record>
      <value>a</value>
      <size>10</size>
    </record><record>
      <value>b</value>
      <size>35</size>
    </record><record>
      <value>c</value>
      <size>60</size>
    </record>
  </group>
</table>

    Incidentally, it is possible to access a constructed node set in a variable if you use the node-set() function which is available in most XSLT processors. I like to avoid the node-set() function when I can because it is non-standard and does not have complete support (and its namespace isn't even consistent across processors that do support it), but here is how you could do it:

    <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                xmlns:exslt="http://exslt.org/common" 
                exclude-result-prefixes="exslt">
  <xsl:output method="xml" indent="yes" omit-xml-declaration="yes"/>
  <xsl:key name="kRecord" match="record" use="name"/>

  <xsl:template match="@* | node()">
    <xsl:copy>
      <xsl:apply-templates select="@* | node()"/>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="/table">
    <xsl:copy>
      <xsl:variable name="groups">
        <xsl:apply-templates
          select="record[generate-id() = 
                         generate-id(key('kRecord', name)[1])]"
          mode="group" />
      </xsl:variable>
      <xsl:apply-templates select="exslt:node-set($groups)/*">
        <xsl:sort select="maxsize" data-type="number" order="descending" />
      </xsl:apply-templates>
    </xsl:copy>
  </xsl:template>

  <xsl:template match="record" mode="group">
    <xsl:variable name="members" select="key('kRecord', name)" />
    <group>
      <xsl:value-of select="name" />
      <maxsize>
        <xsl:apply-templates select="$members/size" mode="max">
          <xsl:sort select="." data-type="number" order="descending" />
        </xsl:apply-templates>
      </maxsize>
      <xsl:apply-templates select="$members" />
    </group>
  </xsl:template>

  <xsl:template match="record/name" />

  <xsl:template match="*" mode="max">
    <xsl:if test="position() = 1">
      <xsl:value-of select="." />
    </xsl:if>
  </xsl:template>
</xsl:stylesheet>