I'd like to use the field calculator in QGIS to create a unique feature (polygon) id that reflects different levels in a geographic hierarchy. So say I have a REGION attribute within which there are several AREAS (unique features). I have alphanumeric codes for the REGIONS, but within each I want to number the AREAS in sequence from 1 to whatever. The order doesn't matter. So the final unique ids would look something like:
GY001, GY002, GY003... DL001, DL002...
If I didn't want to start over again for each REGION, I would just calculate it as
But how to restart the numbering for each REGION?