Yeah, it doesn't work because the sort has to be DIRECTLY after the for-each. The xsl:choose interferes with that. You should set some variables with the chosen sorting options first. I'll post an example in a minute.

Here's your code rewritten, something like this should work:

    <xsl:choose>
      <xsl:when test="umbraco.library:Request('something') = 'something'">
        <xsl:variable name="sortfield" select="./data [@alias = 'this']" />
      </xsl:when>
      <xsl:when test="umbraco.library:Request('something') = 'something'">
        <xsl:variable name="sortfield" select="./data [@alias = 'that']" />
      </xsl:when>
      <xsl:otherwise>
        <xsl:variable name="sortfield" select="./data [@alias = 'another']" />
      </xsl:otherwise>
    </xsl:choose>

    <xsl:call-template name="example">
      <xsl:with-param name="item" select="."/>
      <xsl:with-param name="sortField" select="$sortField" />
    </xsl:call-template>

Then, after the </xsl:template> item add a new template:

  <xsl:template name="example">
    <xsl:param name="item"/>
    <xsl:param name="sortField"/>

    <xsl:for-each select=".">
      <xsl:sort select="$sortField" data-type="number" />
    </xsl:for-each>
  </xsl:template>

Actually, you probably don't need the seperate template, just put the for-each instead of the call-template bit. :)

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