Here is the XSLT 1.0 stylesheet for this (using an extension function,
node-set):

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
xmlns:common="http://exslt.org/common">

<xsl:template match="/list">
 <xsl:variable name="rtf">
   <xsl:for-each select="*">
     <xsl:call-template name="tokenize">
       <xsl:with-param name="string" select="@ids" />
       <xsl:with-param name="delim" select="','" />
     </xsl:call-template>
   </xsl:for-each>
 </xsl:variable>

 <xsl:for-each select="common:node-set($rtf)/token[generate-id() =
generate-id(key('x', .)[1])]">
   <xsl:sort select="." />
   <xsl:value-of select="." />: <xsl:value-of select="count(key('x',
.))" /><xsl:text>&#xa;</xsl:text>
 </xsl:for-each>
</xsl:template>

<xsl:template name="tokenize">
 <xsl:param name="string" />
 <xsl:param name="delim" />

 <xsl:choose>
   <xsl:when test="contains($string, $delim)">
     <token><xsl:value-of select="substring-before($string, $delim)" /></token>
     <xsl:call-template name="tokenize">
       <xsl:with-param name="string" select="substring-after($string,
$delim)" />
       <xsl:with-param name="delim" select="$delim" />
     </xsl:call-template>
   </xsl:when>
   <xsl:otherwise>
     <token><xsl:value-of select="$string" /></token>
   </xsl:otherwise>
 </xsl:choose>
</xsl:template>

Regards,
Mukul

For instance, I have the following XML-File:

<list>
 <item1 ids="a,b,c,e" />
 <item2 ids="b,c,d" />
 <item3 ids="a,c,d,e" />
 <item4 ids="e,f" />
 <item5 ids="a,c,d,e,g" />
</list>

I contemplate how to count the occurences of
(a) all ids (e.g. 'a') in the document and
(b) to count the occurences of a specific (known) id (e.g. 'f') in the document.

For case a the output should be like this:

a: 3
b: 2
c: 4
d: 3
e: 4
f: 1
g: 1

I started to learn XSL yesterday. For several other problems, I found an easily adaptable solution on the web, numerous time on this list here.
But for my current problem, there was no such help available.
Of course, I found here a similar posting which deals with occurences of equal nodes (http://www.stylusstudio.com/xsllist/200309/post20830.html), but I don't know how to adapt it. So please find a solution and help me and others who have the same problem.

Thanks in advance,

S. Renault