You can suppress repeated fields in IReport by going to the repeated field properties box and unchecking the Print Repeated Values box. But how about when an entire subreport is being repeated when there is bad data in one of the fields that causes the subreport to repeat print?

The 2nd print of the subreport can be suppressed by clicking on the subreport box in the master report. Click on properties, and click on the common tab. In the print when expression box at the bottom, enter:

new Boolean($V{REPORT_COUNT}.intValue() ==1)

This will ensure that the subreport is only printed out once.