Control Table Keys In cdata

John Mount announces a new feature in the cdata package:

In our cdata R package and training materials we emphasize the record-oriented thinking and how to design a transform control table. We now have an additional exciting new feature: control table keys.
The user can now control which columns of a cdata control table are the keys, including now using composite keys (that is keys that are spread across more than one column). This is easiest to demonstrate with an example.

Read on for an example of how you can use this.