CODEWITHSUNDEEP
xmlxsltxpath
Pete
Pete

Reputation: 17152

How can I use XSLT to retrieve element closest to but not after a certain date?

Given a list of elements with a date attribute, for example, 

<foo>
 <bar date="2001-04-15"/>
 <bar date="2002-01-01"/>
 <bar date="2005-07-04"/>
 <bar date="2010-11-10"/>
</foo>

I would like to retrieve the element closest to but not after a given date using XSLT.

Calling this function with parameter "2008-01-01" should print <bar date="2005-07-04">. Assume the context node is already <foo>.

I'm not sure what would be easier, but I could also set up three attributes: day, month, year, instead of having one date attribute.

Upvotes: 4

Views: 627

Answers (2)

Daniel Haley
Daniel Haley

Reputation: 52878

Here's an XSLT 2.0 option...

XML Input

<foo>
    <bar date="2001-04-15"/>
    <bar date="2005-07-04"/>
    <bar date="2002-01-01"/>
    <bar date="2010-11-10"/>
</foo>

XSLT 2.0

<xsl:stylesheet version="2.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform" xmlns:xs="http://www.w3.org/2001/XMLSchema">
    <xsl:output indent="yes"/>
    <xsl:strip-space elements="*"/>

    <xsl:param name="threshold" select="xs:date('2008-01-01')"/>

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

    <xsl:template match="foo">
        <xsl:variable name="closestDate" as="node()*">
            <xsl:apply-templates select="bar[$threshold >= xs:date(@date)]">
                <xsl:sort select="@date" data-type="text"/>
            </xsl:apply-templates>                  
        </xsl:variable>
        <xsl:copy-of select="$closestDate[last()]"/>
    </xsl:template>

</xsl:stylesheet>

XML Output

<bar date="2005-07-04"/>

Explanation of "foo" template...

<xsl:template match="foo">
    <!--First a variable named 'closestDate' is created by doing an 
        'xsl:apply-templates' to all 'bar' elements that have a '@date' 
        attribute that is less than or equal to the 'threshold' parameter 
        (which is '2008-01-01' in the example). Notice that both '@date' 
        and '$threshold' are cast as 'xs:date' so that the date comparison 
        will work correctly. Also, we use the 'as="node()*"' attribute to 
        cast the variable as zero or more nodes() so that each individual 
        'bar' can be accessed individually.-->
    <xsl:variable name="closestDate" as="node()*">
        <xsl:apply-templates select="bar[$threshold >= xs:date(@date)]">
            <!--This 'xsl:sort' is used to put all the 'bar' elements in order 
                based on the '@date' attribute.-->
            <xsl:sort select="@date" data-type="text"/>
        </xsl:apply-templates>
    </xsl:variable>
    <!--What we end up with for the 'closestDate' variable is this:
            <bar date="2001-04-15"/>
            <bar date="2002-01-01"/>
            <bar date="2005-07-04"/>
        In the following 'xsl:copy-of', we choose the last node 
        in 'closestDate'.-->
    <xsl:copy-of select="$closestDate[last()]"/>
</xsl:template>

Upvotes: 2

Ian Roberts
Ian Roberts

Reputation: 122394

For XSLT 1.0 this is tricky, as it doesn't support dates as first class values, nor lexicographic comparisons of strings. And it doesn't (per spec) support constructing a node set in a temporary variable and then extracting individual nodes from that set. Nontheless what you want is possible with a few tricks.

The fact that you have your dates as YYYY-MM-DD means that if you strip out the hyphens and treat the resulting string as a number, sorting these numbers in numerical order gives the same result as sorting the original dates in chronological order. And although XSLT doesn't have updateable variables, you can get a similar effect by having a template which recursively applies itself to sibling nodes one by one, passing the state down in template parameters.

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">

<xsl:param name="targetDate" select="20080101" />

<xsl:template match="foo">
  <!-- find the first "candidate" bar whose date is before the target date -->
  <xsl:apply-templates select="(bar[translate(@date, '-', '') &lt; $targetDate])[1]" />
</xsl:template>

<xsl:template match="bar">
  <xsl:param name="closest" select="." />
  <!-- find the next candidate bar whose date is before the target date -->
  <xsl:variable name="nextCandidate"
    select="(following-sibling::bar[translate(@date, '-', '') &lt; $targetDate])[1]" />
  <xsl:choose>
    <xsl:when test="$nextCandidate">
      <xsl:choose>
        <xsl:when test="translate($nextCandidate/@date, '-', '') &gt; translate($closest/@date, '-', '')">
          <!-- $nextCandidate is closer to the target than the current $closest -->
          <xsl:apply-templates select="$nextCandidate">
            <xsl:with-param name="closest" select="$nextCandidate" />
          </xsl:apply-templates>
        </xsl:when>
        <xsl:otherwise>
          <!-- current $closest is still the closest -->
          <xsl:apply-templates select="$nextCandidate">
            <xsl:with-param name="closest" select="$closest" />
          </xsl:apply-templates>
        </xsl:otherwise>
      </xsl:choose>
    </xsl:when>
    <xsl:otherwise>
      <!-- no more candidates, so $closest is the node we require -->
      <xsl:copy-of select="$closest" />
    </xsl:otherwise>
  </xsl:choose>
</xsl:template>


</xsl:stylesheet>

Upvotes: 3

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