Help with function to organise some data

Awesome, thanks, that seems to work! Thank you both so much for your efforts! This will be really useful

EDIT:
Just one more thing...
Say if there were two studies at one site, but both by the same Author and year.
Instead of just displaying the single Author-year e.g.


2 Studies Koram-2008

Would it be possible for it to realize when the author/year is duplicated and make it like:


2 Studies (2)Koram-2008

and


3 Studies Batty-1998, de Vries-2000


to


3 Studies (2)Batty-1998, de Vries-2000

Cheers!