Grouping and avoiding duplicates

Hello all!

Let's see if anybody can help me with this.

My input XML file is of the form:

input.xml
---------

<scl1001>
  ...
  <reg date="2003-11-04">
     <user dept="2" lastacc="2003-11-04 09:13:10.003276">john</user>
     <user dept="2" lastacc="2003-11-04 09:09:23.043209">tom</user>
     <user dept="1" lastacc="2003-11-04 21:31:25.748652">JAMES</user>
  </reg>
  ...
  <reg date="2003-11-07">
     <user dept="1" lastacc="2003-11-07 14:33:33.735231">rob</user>
     <user dept="2" lastacc="2003-11-07 18:58:50.221562">julia</user>
     <user dept="1" lastacc="2003-11-07 22:23:57.772418">JAMES</user>
  </reg>
  <reg date="2003-11-10">
     <user dept="2" lastacc="2003-11-10 10:50:40.438368">tom</usw>
  </reg>
  ...
</scl1001>

The files contains the timestamp of the last login of users on each
day. Each user may log in several times during a day, and may log
in several days. The different <user>'s within each <reg> may not be
ordered. The file contains information of the current year.

I'd like to transform that XML file into another of the following
form:

output.xml
----------

<scl1001>
  ...
  <user dept="1" lastacc="2003-11-07 22:23:57.772418">JAMES</user>
  <user dept="2" lastacc="2003-11-10 10:50:40.438368">tom</usw>
  ...
</scl1001>

Given a year and month (say Nov 2003), output.xml contains the
list of <user> tags, with the most recent login timestamp, thus
each <user> appears just once.

The XSL sheet I'm working on does not exactly generate the
required output, it repeats <user>'s. The problem is in the
first <for-each>.

I don't know how to select distinct <user> tags, that is,
distinct user names (avoid duplicates).

Any hint would be highly appreciated.

Thanks!


Sample output.xml:
------------------

<scl1001>
  ...
  <user dept="2" lastacc="2003-11-10 10:50:40.438368">tom</user>
  <user dept="2" lastacc="2003-11-10 10:50:40.438368">tom</user>
  ...
</scl1001>

This is the XSL file:

month_activity.xsl:
-------------------

(Note: "theDate" is a parameter of the form yyyy-mm)

<xsl:key name="group-by-name" match="user" use="."/>

<xsl:template match="scl1001">
	<scl1001>
	<xsl:for-each select=".//user[substring(@lastacc,1,7)=$theDate]">
		<xsl:sort select="." data-type="text" order="ascending"/>
		<xsl:for-each
select="key('group-by-name',.)[substring(@lastacc,1,7)=$theDate]">
			<xsl:sort select="@lastacc" data-type="text"
order="descending"/>
			<xsl:if test="position() = 1"><xsl:copy-of
select="."/></xsl:if>
		</xsl:for-each>
	</xsl:for-each>
	</scl1001>
</xsl:template>



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