combining idata files

Does anyone have a program or script which will allow me to:

1) "subtract" completely a folder from the idata file, and
2) "add" a folder or folders from another idata file into the main idata
   file.

(I realize that, in general, this is less-than-ideal for statistics purposes.
I was hoping I could use such a mechanism to try to "share" my statistics
with other people, even if it's not as useful as the raw data.)

It would be even nicer if I could combine idata files, adding words where
necessary and adding frequency counts appropriately, but that may be a bit
more tricky.

Thanks.