Sorting in XSL apply-templates nodes using other nodes from a variable (XSLT 1.0)

2
votes

How to sort <foo name="..."/> nodes from $foo using their corresponding node order from $bar?

Partial solution (Mark Veenstra)

<xsl:for-each select="$list-resources">
    <xsl:apply-templates select="$building-resources[@name = current()/@name]">
        <xsl:with-param name="param" select="$some-value"/>
    </xsl:apply-templates>
</xsl:for-each>

New problem (see edit at the end of the question):

How to retrieve the position in the whole sorted node set of each $building-resources node?

TL;DR answer

  • The <xsl:sort/> has an attribute, @data-type, to specify the type of data in the @select node. Default is "text". Since I compare numbers, I must set @data-type="number". Else, the text comparison fails when it comes to compare 9 and 10.

  • <xsl:sort select="count($bar[@name = current()/@name]/preceding-sibling::*)" data-type="number"/>

  • In <xsl:sort/>, current() refers to the currently sorted node (not to the <xsl:template/> current node)

Thanks to michael.hor257k

Complete Answer

Code 

    <!-- Resource "instances" to order, using $list-resources -->
    <xsl:variable name="building-resources"
        select="document('building.xml')/building/resource"/>

    <result>
        <!-- Apply templates to the resource instances -->
        <xsl:apply-templates select="$building-resources">
            <!-- Sort using the nodes order from the resources list -->
            <!-- Don't forget the @data-type: we're comparing NUMBERS not TEXTS -->
            <xsl:sort
                select="count($list-resources[@name = current()/@name]/preceding-sibling::*)"
                data-type="number"/>
        </xsl:apply-templates>
    </result>
</xsl:template>

<!-- Template to apply for each resource of $building-resources -->
<xsl:template match="ressource">
    <!-- position() refers to the node position in $building-resources
    because we used $building-resources as @select value
    of the apply-templates -->
    <output position="{position()}">
        <xsl:value-of select="."/>
    </output>
</xsl:template>

Inputs

list-resources.xml

<resources>
    <resource name="wood"/>
    <resource name="stone"/>
    <resource name="gold"/>
</resources>

building-resources.xml

<building>
    <resource name="stone"/>
    <resource name="gold"/>
    <resource name="stone"/>
    <resource name="wood"/>
    <resource name="wood"/>
</building>

Output

<result>
    <output position="1">wood</output>
    <output position="2">wood</output>
    <output position="3">stone</output>
    <output position="4">stone</output>
    <output position="5">gold</output>
</result>

Original question

Sorting

I have two XML documents:

A list of resources (list-resources.xml, like a "class" list):

<resources>
    <resource name="wood"/>
    <resource name="stone"/>
    <resource name="gold"/>
</resources>

And resources inside a building (buildings.xml, like "objects" list):

<building>
    <resource name="stone"/>
    <resource name="gold"/>
    <resource name="stone"/>
    <resource name="wood"/>
    <resource name="wood"/>
</building>

I want to order the <resource/> nodes from <building/> so it matches the <resource/> order from <resources/>. This is the desired output:

<result>
    <output position="1">wood</output>
    <output position="2">wood</output>
    <output position="3">stone</output>
    <output position="4">stone</output>
    <output position="5">gold</output>
</result>

To do so, I have two node-sets in a XSL:

<xsl:variable name="building-resources" select="building/resource"/>
<xsl:variable name="list-resources" select="resources/resource"/>

And I use an XSL apply-templates to treat nodes from $building-resources:

<xsl:apply-templates select="$building-resources">
    <xsl:with-param name="some-param" select="$variable-from-somewhere"/>
</xsl:apply-templates>

Let's say the applied templates is ok. My currently not-sorted result is:

<result>
    <output position="1">stone</output>
    <output position="2">gold</output>
    <output position="3">stone</output>
    <output position="4">wood</output>
    <output position="5">wood</output>
</result>

Now, I added a <xsl:sort/> element to sort my nodes from $building-resources, but I don't know what to put inside its @select...

<xsl:apply-templates select="$building-resources">
    <xsl:sort select="what-to-put-here"/>
    <xsl:with-param name="some-param" select="$variable-from-somewhere"/>
</xsl:apply-templates>

I tried the following XPath expression:

count($list-ressources[@name = current()/@name]/preceding-sibling::*)

But inside this XPath, current() refers to the node treated by the <xsl:template/> where <xsl:apply-templates/> is. So, instead of current(), But this doesn't work, the result is not correctly sorted. I would mean "the node the <xsl:sort/> process is currently treating" (edit: this is actually exactly what current() does!) inside my XPath brackets $list-resources[]. How do I do so?

Get the sorted position

Since I simplified the code, I forgot something... Mark Veenstra's solution raised up a problem.

In the applied template (the template that generates the <output/> node), I use position() to get the position of the node the template is applied on:

<xsl:template match="resource">
    <xsl:variable name="position" select="position()"/>
    <output position="{$position}">
        <xsl:value-of select="@name"/>
    </output>
</xsl:template>

This works well as long as I do only "one" apply-templates (hence the position() inside the this applied template holds the position of the node in the sorted list). But if I apply Mark's solution (note that current() inside the <xsl:sort/> now refers to the node from the <xsl:for-each/> aka from $liste-resources):

<xsl:for-each select="$list-resources">
    <xsl:apply-templates select="$building-resources[@name = current()/@name]">
        <xsl:with-param name="param" select="$some-value"/>
    </xsl:apply-templates>
</xsl:for-each>

Then the position() inside the applied template refers to the position of the node in the partial node set ($building-resources[@name = current()/@name]).

How to fix that?

3
xmlsortingxsltxpath
stackoverflow.com/questions/1287651/xslt-custom-sort - Mark Veenstra
@MarkVeenstra I don't want to sort $building-resources using one of their own attribute (@name in that other question), but using another node set. So I don't get how these questions could be related. - Xenos
Please indicate XSLT 1.0 or 2.0. - michael.hor257k

3 Answers

2
votes

I think you should try to do something like the following. (untested)

Change:

<xsl:apply-templates select="$building-resources">
    <xsl:sort select="what-to-put-here"/>
    <xsl:with-param name="some-param" select="$variable-from-somewhere"/>
</xsl:apply-templates>

To:

<xsl:for-each select="$list-resources/@name">
    <xsl:variable name="curName" select="." />
    <xsl:apply-templates select="$building-resources[@name = $curName]">
        <xsl:with-param name="some-param" select="$variable-from-somewhere"/>
    </xsl:apply-templates>
</xsl:for-each>

So before applying the templates, make sure you apply in the order of the other nodeset. That's why I added an extra for-each around it.

2
votes

Regarding the sorting problem, I would suggest:

<xsl:stylesheet version="1.0" 
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>

<xsl:template match="/">
    <building>
        <xsl:apply-templates select="building/resource">
            <xsl:sort select="count(document('list-resources.xml')/resources/resource[@name = current()/@name]/preceding-sibling::resource)" data-type="number" order="ascending"/>
        </xsl:apply-templates>
    </building>
</xsl:template>

<xsl:template match="resource">
    <resource position="{position()}">
        <xsl:value-of select="@name"/>
    </resource>
</xsl:template>

</xsl:stylesheet>

Applied to your input example, this returns:

<?xml version="1.0" encoding="UTF-8"?>
<building>
   <resource position="1">wood</resource>
   <resource position="2">wood</resource>
   <resource position="3">stone</resource>
   <resource position="4">stone</resource>
   <resource position="5">gold</resource>
</building>

I am not sure what the other problem is.

0
votes

I'd use an XSL key and <xsl:sort>, like this:

<xsl:key name="kResource" match="resources/resource" use="@name" />

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

<!-- specialized identity template, adds a position attribute -->
<xsl:template match="*" mode="with-position">
  <xsl:copy>
    <xsl:attribute name="position"><xsl:value-of select="position()" /></xsl:attribute>
    <xsl:apply-templates select="node() | @*" />
  </xsl:copy>
</xsl:template>

<xsl:template match="building">
  <result>
    <xsl:apply-templates select="*" mode="with-position">
      <xsl:sort select="count(key('kResource', @name)/preceding-sibling::*)" data-type="number" />
    </xsl:apply-templates>
  </result>
</xsl:template>

Relevant output:

<result>
  <resource position="1" name="wood" />
  <resource position="2" name="wood" />
  <resource position="3" name="stone" />
  <resource position="4" name="stone" />
  <resource position="5" name="gold" />
</result>

Note that even though I've added a position attribute, I think that's a rather unnecessary thing to have. XML elements have a natural position in the document, no need to be over-specific.