reporting services - Format field based on number of rows - Report Designer 1.0 -

i have table in report designer 1.0. in 'file' column there multiple entries same file name. each of these entries in 'total file header' column i'd replace amounts "n/a", except last entry. example:

currently:

    file1     $655.12     file1     $655.12     file1     $655.12     file1     $655.12     file1     $655.12     file2     $59.33     file2     $59.33     file3     $124.12      file3     $124.12     file3     $124.12     file3     $124.12     file3     $124.12     file4     $12.33     file5     $44.64  i'd have:      file1     n/a     file1     n/a     file1     n/a     file1     n/a     file1     $655.12     file2     n/a     file2     $59.33     file3     n/a      file3     n/a     file3     n/a     file3     n/a     file3     $124.12     file4     $12.33     file5     $44.64 

i tried following, didn't work. tips?

=iif(count(fields!ama_filenamekey.value)<countrows(fields!ama_filenamekey.value),"n/a",val(fields!totalpointsoffile.value)) 

try this.

=iif(rownumber("datasetgroup")<countrows("datasetgroup"),"n/a",fields!totalpointsoffile.value) 

i prefer solving in dataset (or sql) instead of formatting(or fixing) in report designer.