Auto Generate Unique Sequential Project Code by Sectors

I have a list of unique projects with actual project names. Each project belongs to a Sector (Retail, Commercial, Office, etc). 

In one of our report, the intention is to provide a report info without giving away the actual project name.

I would like to have a functionality that automatically generate a Generic Project Name based on the Sector it is in. 

For example:

Actual project names
Retail Shop John
Commercial Tower Apple
Commercial Google
Office Project Jane

Generic Project names
Retail 0001
Commercial 0001
Commercial 0002
Office 0001

The above fields is in a table called Projects
The sector names are now in a dropdown list field on a separate table on its own called Sectors

I have created a 2 fields - Project & Project_Generic but not sure how to move forward. 

Any help is much appreciated.

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Nigel
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