Question

I need to change the order in which my for-each is executed only if some conditions are met.

Here is what my XML looks like :

<OptionList>
    <Option name="My First Option" />
    <Option name="My Second Option" />
</OptionList>

However, in some case, my XML can be like this :

<OptionList>
    <Option />
    <Option name="My Second Option" />
</OptionList>

In my XSL, I’m doing a for-each like this :

<xsl:for-each select="//OptionList/Option">
    {...}
</xsl:for-each>

I know I can change orders of Option nodes using this line in my for-each :

<xsl:sort select="position()" data-type="number" order="descending" />

The problem is that I want my order to be descending only when my first Option node is empty and doesn’t have the name attribute. Otherwise, I want to keep the default ascending order.

Any input on how I can acheive that? So far, everything I tried ended up with “Variable out of scope” or invalid use of xpath functions.

Answer 1

You can use a hack to change the sort order based on a condition:

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

  <xsl:template match="/">
    <result>
    <xsl:for-each select="//OptionList/Option">
      <xsl:sort data-type="number" order="ascending"
        select="position()*(-2*number(not(//OptionList/Option[1]/@name))+1)"/>

      <option>
        <xsl:value-of select="@name"/>
      </option>
    </xsl:for-each>
    </result>

  </xsl:template>
</xsl:stylesheet>

The hack is that number((true()) returns 1 and number(false()) returns 0. As a consequence, the expression

-2 * number(not(//OptionList/Option[1]/@name)) + 1

evaluates to 1 if the first option element has a name attribute and to -1 otherwise. This is used as a factor to reverse the sort order.