merge 3 data sets with different identifiers, one string identifier

Good day all,

I have 3 datasets A,B and C. Dataset B and C I want to merge certain variables to dataset A.

Dataset B I can merge with no issues by using id and year.

Dataset C has a unique identifier which is a string variable. I thought of encoding this variable in dataset A and C but the code is not the same in each dataset.

Does anyone know how I can best resolve this issue?

Kind regards,

Joshua