InfoPath Dev

Hello all,

I have been asked to develop an InfoPath Form that displays a report based on information that is housed in an Access Data Base.  I have had our programmers create a WebService that allows me to query said Data Base with a Start and End Date.  The WebService returns all of the information that falls within that date range.

I have displayed the repeating table from the Data Connection on the Form and it is returning all of the information that falls within that date range when I set the dates and query the Data Connection.

I now need to create a field which displays a Count for all of the participants who have performed a mission within that date range.  However when a participant has completed multiple missions within that data range.  I do not want to count them multiple times.  I only want to count that particular Participant_Name once.  Because this report only cares about how many different people were asked to participate in missions between that date range.

So what I will need is to be told how to count only unique items within a repeating table from a Data Connection that I do not have the ability to create new fields within.  I have tried: count(Participant_Name[preceding-sibling::* != Participant_Name]) but that does not return the correct count.

I have spent several days with googe, try, fail and so am now onto the forums, lol.  I would appreciate any advice.

Thank you