XPath: Selecting from a nodeset returned from a function

Question

I'm just starting out with XSLT, so bear with me. I am processing a fairly complex document with a structure similar to the one below. It is divided into two sections, data and meta. For each data/item I need to look up the "actual" class in the corresponding meta/item.

<root>
  <data>
    <item id="i1">
      <h3 id="p2">akkakk</h3>
      <p id="p3">osijaoid</p>
      <p id="p4">jqidqjwd</p>
    <item>
  </data>
  <meta>
    <item ref="i1">
      <p ref="p2" class="heading"/>
      <p ref="p3" class="heading"/>
      <p ref="p4" class="body"/>
    </item>
  </meta>
</root>

I need to group adjacent p elements in meta on their class attribute. I thought a helper function could make this a bit cleaner:

<xsl:function name="fn:node-groups" as="node()*">
  <xsl:param name="parent"/>
  <xsl:variable name="nodeRefs" select="root($parent)//meta/item[@ref = $parent/@id]/p"/>
  <xsl:for-each-group select="$nodeRefs" group-adjacent="@class">
    <group class="{@class}">
      <xsl:for-each select="current-group()">
        <node ref="{@ref}"/>
      </xsl:for-each>
    </group>
  </xsl:for-each-group>
</xsl:function>

And then use it when processing the data nodes, like so. My problem is that I can not select further from the nodeset returned by the function.

<xsl:template match="//data/item">
  <!-- works -->
  <xsl:variable name="test1" select="fn:node-groups(.)"/>
  <!-- works -->
  <xsl:variable name="test2" select="fn:node-groups(.)/*"/>
  <!-- does not work -->
  <xsl:variable name="test3" select="fn:node-groups(.)/group[@class = 'heading']"/>
</xsl:template>

I can write a star as in test2, and that gives me all node nodes. But anything else just gives me an empty nodeset. Or at least it looks that way, but at this point I really don't know anymore.

Martin Honnen · Accepted Answer · 2016-11-28 21:55:13Z

1

I suppose your stylesheet has an xmlns="http://example.com/foo" namespace declaration scope for the function that puts the result elements in the function in that namespace and then obviously fn:node-groups(.)/group will not select them as it selects a group element in no namespace. So make sure your function overrides that namespace with <xsl:for-each-group select="$nodeRefs" group-adjacent="@class" xmlns="">.

Another reason could be that your stylesheet defines xpath-default-namespace.

I also think that your third variable needs to be <xsl:variable name="test3" select="mf:node-groups(.)/node"/> as obviously the node sequence returned by your function already is a sequence of group elements, if you want to filter that sequence then use <xsl:variable name="test3" select="fn:node-groups(.)[@class = 'heading']"/>

edited Nov 28, 2016 at 21:55

answered Nov 28, 2016 at 14:53

Martin Honnen

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1 Comment

svenax Over a year ago

Thank you! The problem was as of course that I needed to select fn:node-groups(.)/[@class = 'heading'] instead of fn:node-groups(.)/group[@class = 'heading']. Sometimes you get stuck and need a nudge in the right direction to be able to go on.

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