Getting a count of values that show up at least once

[Andrew Serff]

Hello,

I have some example metrics that I'm using to model real metrics we will be
generating from our application and I'm trying to build some xqueries to
help extract the data we want from the metrics, but I'm having problems
wrapping my head around this one.  Here is some of the sample metrics:

<metrics>
    <metric>
        <hostname><![CDATA[myhost]]></hostname>
        <category><![CDATA[FIGHT MOVE]]></category>
        <name><![CDATA[Martial Art Action 0]]></name>
        <description><![CDATA[chucknorris just landed a slap on
chucknorris]]></description>
        <time_elapsed>36800</time_elapsed>
        <application><![CDATA[UFC]]></application>
        <action><![CDATA[SLAP]]></action>
        <timestamp>2010-05-14T09:02:33</timestamp>
        <user><![CDATA[chucknorris]]></user>
    </metric>
    <metric>
        <hostname><![CDATA[myhost]]></hostname>
        <category><![CDATA[FIGHT MOVE]]></category>
        <name><![CDATA[Martial Art Action 1]]></name>
        <description><![CDATA[jetlee just landed a roundhouse on
chucknorris]]></description>
        <time_elapsed>35245</time_elapsed>
        <application><![CDATA[UFC]]></application>
        <action><![CDATA[ROUNDHOUSE]]></action>
        <timestamp>2010-05-14T09:02:33</timestamp>
        <user><![CDATA[jetlee]]></user>
    </metric>
    <metric>
        <hostname><![CDATA[myhost]]></hostname>
        <category><![CDATA[FIGHT MOVE]]></category>
        <name><![CDATA[Martial Art Action 2]]></name>
        <description><![CDATA[chucknorris just landed a kick on
jetlee]]></description>
        <time_elapsed>43474</time_elapsed>
        <application><![CDATA[UFC]]></application>
        <action><![CDATA[KICK]]></action>
        <timestamp>2010-05-14T09:02:33</timestamp>
        <user><![CDATA[chucknorris]]></user>
    </metric>
</metrics>

What I would like to pull out of this is how many unique users there were
per action (i.e. How many people Kicked someone today).  So I've stared of
by getting a list of all the unique Actions:
for $value in
(distinct-values(collection('metricsCollection.xml')//metrics/metric/action))
and a list of all the unique users for that action:
for $user in
(distinct-values(collection('metricsCollection.xml')//metrics/metric[action
= $value]/user))

That is where I get stuck.  I just want to count which users show up at
least once and then output something like:
<mertics>
  <metric>
    <action>KICK</action>
    <num_users>5</num_users>
  </metric>
  <metric>
    <action>SLAP</action>
    <num_users>2</num_users>
  </metric>
</metrics>

if I do:
count(collection('metricsCollection.xml')//metrics/metric[action = $value
and user = $user])
I just get a count of all the nodes that have that value and user.  I've
been trying to figure out how to just add 1 to some counter like you would
in java for example, but it seems you can't increment values in xquery
because once you define a variable it never changes.

Does anyone have any hints/advice for me?

Thanks!
Andrew
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