Calculating totals of only specific criteria of fields

[*LEECE*]

I am trying to carry out a similar function to that of the excel version
"count .... if"

I have a sales form, with lets say 6 different sales types. On completing
the form, I have a whole list of sales orders on my form, all with one of the
6 sales types allocated to it. I then wnat Infopath to add the costs of all
Sales Types 1, then Sales Type 2 etc... so that I have costs by sales type
automatically calculated for me.

 

[mmattson]

I use the following XPath script and get ""my:WhenIfDate" does not point to
a valid location path of a field or group."

I am trying to calculate only found records in a query.

sum(d:Sick_Trans/@UnitsReceived[d:Sick_Trans/@TransactionDate <
.../../my:WhenIfDate])