xslt completely remove duplicates from string - html

Question

I have a variable containing non-numerical values, and I need to completely remove duplicate entries from this string using XSLT:
$string = a,b,c,c,d,d,e,f,g
needs to become: $newstring = a,b,e,f,g
An alternative option would be to compare the two variables and ignore/remove the overlapping entries.
$stringA = a,c
$stringB = a,b,c,d,e,f
needs to become:
$newstring = b,d,e,f
Concatenating the variables is straightforward but I need the opposite of that!
Please help,

Answer 1

XSLT is designed to process XML, not strings. XSLT 1.0 in particular is a poor tool for manipulating text.
IMHO, the best way to proceed here is to convert the problem to XML first. If you're using libxslt (as xsltproc does), this is quite easy to do using an extension function:
XSLT 1.0
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:str="http://exslt.org/strings"
extension-element-prefixes="str">
<xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/>
<xsl:param name="stringA">a,c,g</xsl:param>
<xsl:param name="stringB">a,b,c,d,e,f</xsl:param>
<xsl:variable name="setA" select="str:tokenize($stringA, ',')" />
<xsl:variable name="setB" select="str:tokenize($stringB, ',')" />
<xsl:template match="/">
<test>
<xsl:for-each select="$setA[not(.=$setB)] | $setB[not(.=$setA)]">
<xsl:value-of select="."/>
<xsl:if test="position()!=last()">,</xsl:if>
</xsl:for-each>
</test>
</xsl:template>
</xsl:stylesheet>
Result:
<?xml version="1.0" encoding="UTF-8"?>
<test>g,b,d,e,f</test>