Xpath - get maximum attribute for each element

Question

Given the following XML, what Xpath 2.0 query will get me the maximum date for each contact? My goals ito find contacts who haven't been touched in 30 days.

<contacts>
  <contact>
    <name>james</name>
    <touch method='email' date='2002-02-04'>a</touch>
    <touch method='meeting' date='2010-02-04'>b</touch>
  </contact>
  <contact>
    <name>bob</name>
    <touch method='phone' date='2001-02-04'>y</touch>
    <touch method='email' date='2009-02-04'>d</touch>
  </contact>
  <contact>
    <name>cindy</name>
    <touch method='email' date='2012-02-04'>v</touch>
    <touch method='phone' date='2012-02-04'>h</touch>
  </contact>
  <contact>
    <name>john</name>
  </contact>
</contacts>

max((//@date/xs:dateTime(.))) will get me a single maximum date but I'm trying to get three dates.

Answer 1

Easier version.

You generally do not need to for-in-return for sequences of nodes, as / does the same.

/contacts/contact/max(.//@date/xs:dateTime(.))

and to find the contact before a limit:

/contacts/contact[max(.//@date/xs:dateTime(.)) < '2013-05-04']

Answer 2

Use for as you want to get the maximum value for each contact

for $x in /contacts/contact return max($x//@date/xs:dateTime(.))