Question: I have this XML file, from which I'd like to count the number of users referenced in it. But they can appear in more than one category, and I'd like these duplicates not to be taken into account.  

In the example below, the query should return 3 and not 4. Is there a way in XPath to do so? Users are not sorted at all.

```
<list>
  <group name='QA'>
    <user name='name1'>name1@email</user>
    <user name='name2'>name2@email</user>
  </group>
  <group name='DEV'>
    <user name='name3'>name3@email</user>
    <user name='name2'>name2@email</user>
  </group>
</list>

```

Answer: 
**A pure XPath 1.0 -- one-liner**:

**Use**:

`count(/*/group/user[not(. = ../following-sibling::group/user)])`
using the functions namespace <http://www.w3.org/2005/xpath-functions> you can use 

```
distinct-values(//list/group/user)

```

UPDATE:

At the top of your xsl/xslt file you should have a stylesheet element, map the url above to the prefix `fn` as below...

```
<xsl:stylesheet version="1.0"
 xmlns:fn="http://www.w3.org/2005/xpath-functions"
 >

```

then you can use

```
select="fn:distinct-values(//list/group/user)"

```

this would assume you are doing this in templates and not in some xpathdocument object inwhich case you need to use a namespacemanager class.

links...

[XSLT: Add namespace to root element](https://stackoverflow.com/questions/2686650/xslt-add-namespace-to-root-element)

<http://www.xqueryfunctions.com/xq/fn_distinct-values.html>

<http://msdn.microsoft.com/en-us/library/d6730bwt(VS.80).aspx>

**Otherwise** try Dimitre Novatchev's answer.