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Asked: 2026-05-29T23:55:18+00:00

I’m looking for a way to select a unique set of nodes from an

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I’m looking for a way to select a unique set of nodes from an ancestor element below the root. My simplified input looks like this (Note: there may be several <Single> and <Multi> elements in a <Package>):

<Package>
  <Single>
    <Patient>
      <Drug>
        <Name>A</Name>
        <Dose>1 tab</Dose>
      </Drug>
      <Drug>
        <Name>B</Name>
        <Dose>2 spoonfuls</Dose>
      </Drug>
    </Patient>
  </Single>
  <Multi>
    <Patient>
      <Drug>
        <Name>A</Name>
        <Dose>1 tab</Dose>
      </Drug>
      <Drug>
        <Name>B</Name>
        <Dose>2 spoonfuls</Dose>
      </Drug>
      <Drug>
        <Name>C</Name>
        <Dose>3 drops</Dose>
      </Drug>
    </Patient>
    <Patient>
      <Drug>
        <Name>B</Name>
        <Dose>2 spoonfuls</Dose>
      </Drug>
      <Drug>
        <Name>B</Name>
        <Dose>2 spoonfuls</Dose>
      </Drug>
      <Drug>
        <Name>C</Name>
        <Dose>3 drops</Dose>
      </Drug>
      <Drug>
        <Name>D</Name>
        <Dose>4 glasses</Dose>
      </Drug>
    </Patient>
  </Multi>
</Package>

I’d like to select the Drugs that are unique for each <Single> or <Multi> element accross <Patient>s. So far I have:

  <xsl:template match="/">
    <xsl:for-each select="Package/Single | Package/Multi">
      <xsl:call-template name="SO" />
    </xsl:for-each>
  </xsl:template>

  <xsl:key name="uniqueKey" match="//Patient/Drug" use="concat(Name, Dose)" />

  <xsl:template name="SO">
    <UniquePerMultiOrSingle>
      <xsl:for-each select="//Patient/Drug[
                              generate-id() =
                              generate-id(key('uniqueKey', concat(Name, Dose))[1])]">
        <xsl:copy-of select="Name"/>
        <xsl:copy-of select="Dose"/>
      </xsl:for-each>
    </UniquePerMultiOrSingle>
  </xsl:template>

The output looks like this:

<UniquePerMultiOrSingle>
  <Name>A</Name>
  <Dose>1 tab</Dose>
  <Name>B</Name>
  <Dose>2 spoonfuls</Dose>
  <Name>C</Name>
  <Dose>3 drops</Dose>
  <Name>D</Name>
  <Dose>4 glasses</Dose>
</UniquePerMultiOrSingle>
<UniquePerMultiOrSingle>
  <Name>A</Name>
  <Dose>1 tab</Dose>
  <Name>B</Name>
  <Dose>2 spoonfuls</Dose>
  <Name>C</Name>
  <Dose>3 drops</Dose>
  <Name>D</Name>
  <Dose>4 glasses</Dose>
</UniquePerMultiOrSingle>

The desired output should look like this:

<UniquePerMultiOrSingle>
  <Name>A</Name>
  <Dose>1 tab</Dose>
  <Name>B</Name>
  <Dose>2 spoonfuls</Dose>
</UniquePerMultiOrSingle>
<UniquePerMultiOrSingle>
  <Name>A</Name>
  <Dose>1 tab</Dose>
  <Name>B</Name>
  <Dose>2 spoonfuls</Dose>
  <Name>C</Name>
  <Dose>3 drops</Dose>
  <Name>D</Name>
  <Dose>4 glasses</Dose>
</UniquePerMultiOrSingle>

My question: is there a way to select <Drug>s that are unique per <Single> or <Multi> element only (not the whole document)? If not, is there any other way to achieve this? I’m using xslt 1.0.

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1 Answer

  1. Editorial Team

    This transformation:

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

 <xsl:key name="kPackageDrugsByName" match="Drug"
  use="concat(generate-id(../..), '+', Name, '+', Dose)"/>

 <xsl:template match="Single | Multi">
  <xsl:text>&#xA;</xsl:text>
  <xsl:value-of select="name()"/> -- Drugs:&#xA;<xsl:text/>

  <xsl:copy-of select=
   "*/Drug
       [generate-id()
       =
        generate-id(key('kPackageDrugsByName',
                        concat(generate-id(../..),
                               '+', Name, '+', Dose)
                       )[1]
                   )
       ]/*"/>
 </xsl:template>
</xsl:stylesheet>

    when applied on the provided XML document:

    <Package>
    <Single>
        <Patient>
            <Drug>
                <Name>A</Name>
                <Dose>1 tab</Dose>
            </Drug>
            <Drug>
                <Name>B</Name>
                <Dose>2 spoonfuls</Dose>
            </Drug>
        </Patient>
    </Single>
    <Multi>
        <Patient>
            <Drug>
                <Name>A</Name>
                <Dose>1 tab</Dose>
            </Drug>
            <Drug>
                <Name>B</Name>
                <Dose>2 spoonfuls</Dose>
            </Drug>
            <Drug>
                <Name>C</Name>
                <Dose>3 drops</Dose>
            </Drug>
        </Patient>
        <Patient>
            <Drug>
                <Name>B</Name>
                <Dose>2 spoonfuls</Dose>
            </Drug>
            <Drug>
                <Name>B</Name>
                <Dose>2 spoonfuls</Dose>
            </Drug>
            <Drug>
                <Name>C</Name>
                <Dose>3 drops</Dose>
            </Drug>
            <Drug>
                <Name>D</Name>
                <Dose>4 glasses</Dose>
            </Drug>
        </Patient>
    </Multi>
</Package>

    produces the wanted, correct result:

    Single -- Drugs:
<Name>A</Name>
<Dose>1 tab</Dose>
<Name>B</Name>
<Dose>2 spoonfuls</Dose>

Multi -- Drugs:
<Name>A</Name>
<Dose>1 tab</Dose>
<Name>B</Name>
<Dose>2 spoonfuls</Dose>
<Name>C</Name>
<Dose>3 drops</Dose>
<Name>D</Name>
<Dose>4 glasses</Dose>
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