Custom order and filter - xslt

Question

I have a SharePoint list with news items. From that, I want to be able to select articles, and change the order of the selected items to make some kind of a newsletter.
I tried using a query-string to specify item-IDs and their order, something like this:
SortFilter.aspx?selection='i13o1,i5o2,i27o3,'
( i is for Item, o is for Order)
The filtering works ok, but I can't figure out how to sort using $elementLookup
<xsl:param name="QUERY_STRING" />
<xsl:variable name="string" select= 'substring-before(substring-after($QUERY_STRING, "&apos;"), "&apos;")'/>
<xsl:key name="myKey" match="Row" use="#ID" />
<xsl:template match="/">
<xsl:for-each select="/dsQueryResponse/Rows/Row[generate-id(.)=generate-id(key('myKey',#ID))]">
<xsl:variable name="articleNumber">
<xsl:text>i</xsl:text><xsl:value-of select="#ID" /><xsl:text>o</xsl:text>
</xsl:variable>
<xsl:variable name="elementLookUp" select= 'substring-before(substring-after($string, $articleNumber), ",")'/>
<xsl:if test="$elementLookUp">
<xsl:value-of select="#ID" />
<xsl:text> </xsl:text>
<xsl:value-of select="#Title" />
<xsl:text> </xsl:text>
<xsl:value-of select="$elementLookUp"/>
</xsl:if>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>

Answer 1

You should be able to do so like this:
<xsl:sort
select="substring-before(substring-after($string, concat('i', #ID, 'o')), ',')"
data-type="number" />
This expression will select the number that comes after i<id>o, and then you can sort on that.
After a bit of tidying, your stylesheet becomes:
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:param name="QUERY_STRING" />
<xsl:variable
name="selection"
select='substring-before(substring-after($QUERY_STRING, "selection=&apos;"), "&apos;")'/>
<xsl:key name="myKey" match="Row" use="#ID" />
<xsl:template match="/">
<xsl:for-each
select="/dsQueryResponse/Rows/Row[generate-id(.)=generate-id(key('myKey',#ID)[1])]">
<xsl:sort
select="substring-before(substring-after($selection, concat('i', #ID, 'o')), ',')"
data-type="number"
/>
<xsl:variable name="articleNumber" select="concat('i', #ID, 'o')" />
<xsl:variable name="elementLookUp"
select='substring-before(substring-after($selection, $articleNumber), ",")'/>
<xsl:if test="$elementLookUp">
<xsl:value-of select="#ID" />
<xsl:text> </xsl:text>
<xsl:value-of select="#Title" />
<xsl:text> </xsl:text>
<xsl:value-of select="$elementLookUp"/>
</xsl:if>
</xsl:for-each>
</xsl:template>
</xsl:stylesheet>