Is it possible to not restrict the trap to the R's section of the report, but to also trap earlier in the file, to avoid the error? Then you could create a filter in the table to get back to the desired selection.
Sample - - - - 1
Trap line - A123
Sample - - - - 32,001
Trap line - R456
If you were trapping on a literal "R" in column 13 of line 2, replacing the R with a "A" (that's the alpha trap), and creating a filter of substr(TrapLine;13;1)="R" should give you the same result.