Matrix Field: How to ensure that all input answers are unique per submission

Students have to rank 76 subject groups and each subject group can only be chosen once. 

In each field, they have to use a code. They need to type in instead of using a pull down menu as with 76 choices, the pull down menu will become to long.

Unfortunately, we do not provide unique value validation option for a Matrix field type. We would like to recommend you to stick with the Orderable List widget.

If you need any further assistance, please let us know.