Reorder nodes returned from xsl:choose - xslt

Question

What would be an efficient way to reorder a group of nodes selected using xsl:choose (XSLT 1.0).
Below is the sample source XML:
<Universe>
<CObj>
<Galaxies>
<Galaxy>
<Profile>
<Name>MilkyWay</Name>
<Age>12.5</Age>
</Profile>
<PlanetarySystem>
<Name>Solar</Name>
<Location></Location>
<Planet>
<Name>Earth</Name>
<Satellite>Y</Satellite>
...
...
...
</Planet>
...
...
...
</PlanetarySystem>
<PlanetarySystem>
...
...
...
</PlanetarySystem>
</Galaxy>
<Galaxy>
...
...
...
</Galaxy>
</Galaxies>
</CObj>
</Universe>
XSL snippet:
<xsl:template name="get-galaxy-types">
<xsl:variable name="galaxy_age1" select ="1" />
<xsl:variable name="galaxy_age2" select ="5" />
<xsl:variable name="galaxy_age3" select ="10" />
<xsl:for-each select="Galaxies/Galaxy/Profile/Age">
<xsl:choose>
<xsl:when test=".=$galaxy_age2">
<GalaxyType2>
<xsl:value-of select="../Profile/Name"/>
</GalaxyType2>
</xsl:when>
<xsl:when test=".=$galaxy_age3">
<GalaxyType3>
<xsl:value-of select="../Profile/Name"/>
</GalaxyType3>
</xsl:when>
<xsl:when test=".=$galaxy_age1">
<GalaxyType1>
<xsl:value-of select="../Profile/Name"/>
</GalaxyType1>
</xsl:when>
</xsl:choose>
</xsl:for-each>
Above XSL template is called from main template like:
<xsl:template match="Universe">
<GalaxyTypes>
<xsl:call-template name="get-galaxy-types"/>
</GalaxyTypes>
</xsl:template>
Output XML:
Note that the order of <GalaxyType> cannot be changed.
<Universe>
...
...
...
<GalaxyTypes>
<GalaxyType2>xxxxxx</GalaxyType2>
<GalaxyType3>xxxxxx</GalaxyType3>
<GalaxyType1>xxxxxx</GalaxyType1>
</GalaxyTypes>
...
...
...
</Universe>
Since xsl:choose returns the XML nodes as and when it finds a match I am unable to find a straight forward way to control the order in which I want GalaxyType to appear in the output XML.
How can I have a generic template to perform reordering for any elements that might get added in the future that may fall in to similar requirement. I am fine with having a remapping template within this XSL but I am not really sure how to accomplish this in a really elegant and efficient way.

Answer 1

I am going to guess you want to put the galaxies matching galaxy-age1 first, then the ones matching galaxy-age2 next, and finally the ones for galaxy-age3. I am also assuming the ages specified may not be in ascending order (that is to say, galaxy-age3 could be less that galaxy-age1.
To start with, it might be more natural to do your xsl:for-each over the Galaxy elements
<xsl:for-each select="Galaxies/Galaxy">
Then, to do your customisable sort, you could first define a variable like so...
<xsl:variable name="sortAges"
select="concat('-', $galaxy_age1, '-', $galaxy_age2, '-', $galaxy_age3, '-')" />
Note the order the parameters appear in the concat statement corresponds to the order they need to be output.
Then, your xsl:for-each could look this this...
<xsl:for-each select="Galaxies/Galaxy">
<xsl:sort select="string-length(substring-before($sortAges, concat('-', Profile/Age, '-')))" />
But this is not very elegant. It might be better to simply have a template that matches Galaxy and use three separate xsl:apply-templates to select the Galaxy; one for each age.
Try this XSLT too
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes" />
<xsl:param name="galaxy_age1" select="1" />
<xsl:param name="galaxy_age2" select="5" />
<xsl:param name="galaxy_age3" select="10" />
<xsl:template match="Universe">
<GalaxyTypes>
<xsl:apply-templates select="Galaxies/Galaxy[Profile/Age = $galaxy_age1]">
<xsl:with-param name="num" select="1" />
</xsl:apply-templates>
<xsl:apply-templates select="Galaxies/Galaxy[Profile/Age = $galaxy_age2]">
<xsl:with-param name="num" select="2" />
</xsl:apply-templates>
<xsl:apply-templates select="Galaxies/Galaxy[Profile/Age = $galaxy_age3]">
<xsl:with-param name="num" select="3" />
</xsl:apply-templates>
</GalaxyTypes>
</xsl:template>
<xsl:template match="Galaxy">
<xsl:param name="num" />
<xsl:element name="Galaxy{$num}">
<xsl:value-of select="Profile/Name"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>
EDIT: To make this more efficient, consider using a key to look up the Galaxy elements by their name. Try this XSLT too
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:output omit-xml-declaration="yes" indent="yes" />
<xsl:param name="galaxy_age1" select="1" />
<xsl:param name="galaxy_age2" select="10" />
<xsl:param name="galaxy_age3" select="5" />
<xsl:key name="galaxy" match="Galaxy" use="Profile/Age" />
<xsl:template match="Universe">
<GalaxyTypes>
<xsl:apply-templates select="key('galaxy', $galaxy_age1)">
<xsl:with-param name="num" select="1" />
</xsl:apply-templates>
<xsl:apply-templates select="key('galaxy', $galaxy_age2)">
<xsl:with-param name="num" select="2" />
</xsl:apply-templates>
<xsl:apply-templates select="key('galaxy', $galaxy_age3)">
<xsl:with-param name="num" select="3" />
</xsl:apply-templates>
</GalaxyTypes>
</xsl:template>
<xsl:template match="Galaxy">
<xsl:param name="num" />
<xsl:element name="Galaxy{$num}">
<xsl:value-of select="Profile/Name"/>
</xsl:element>
</xsl:template>
</xsl:stylesheet>

Answer 2

It's very difficult to navigate between the scattered snippets of your code. Still, it seems to me you should change your strategy to something like:
<xsl:template match="?">
...
<GalaxyTypes>
<xsl:apply-templates select="??/???/Galaxy">
<xsl:sort select="Profile/Age" data-type="number" order="ascending"/>
</xsl:apply-templates=>
</GalaxyTypes>
...
</xsl:template>
<xsl:template match="Galaxy">
<xsl:choose>
<xsl:when test="Profile/Age=$galaxy_age1">
<GalaxyType1>
<xsl:value-of select="Profile/Name"/>
</GalaxyType1>
</xsl:when>
<xsl:when test="Profile/Age=$galaxy_age2">
<GalaxyType2>
<xsl:value-of select="Profile/Name"/>
</GalaxyType2>
</xsl:when>
<xsl:when test="Profile/Age=$galaxy_age3">
<GalaxyType3>
<xsl:value-of select="Profile/Name"/>
</GalaxyType3>
</xsl:when>
</xsl:choose>
</xsl:template>
--
Note that your output would be much better formatted if all galaxies were a uniform <Galaxy> element, with a type attribute to tell them apart.