InfoPath Dev

Imagine we have two concatenated fields.

Field1: John;George;Mike;

Field2: Mike;Paul;John;Frank;

 

I would like to compare the individual values in these two fields (arrays if you will) and after comparison, store it in Field3.

Field3: John;Mike;

 

Is this doable with InfoPath without custom code?

I can't think of an easy way. It may be possible to use rules to individually check each name from field 1 - but I'm worried any rule based mechanism would run into looping issues.