Help with function to organise some data

Alright it's pretty hard to concisely describe what I want to do in just the title, I'll outline what I've got and what I want to do.

I'm mapping study site locations of clinical trials. I have lists of data of the Author of the article on the study, the year, the study location, and lattitude and longitude coordinates.
I can make a map where it plots the study locations and shows the Author and year when you mouseover on a site.
You can have a look here:
http://www.gpsvisualizer.com/display...80.170.85.html

The problem is when there are multiple studies at a single location, with this method you cannot see all the different authors of the different studies there. So for the sites where there are multiple studies, I want to list the authors and years.

Currently my source data is in the format of something like:

Author-Year --------Site---------Count
Sutanto-2009---------------Site A-------3
Maguire-2006---------------Site B-------2
Maguire-2006---------------Site A-------3
Baird-1995------------------Site B-------2
Baird-1995------------------Site C-------2
Murphy-1993----------------Site D-------2
Fryauff-1997----------------Site E -------1
Fryauff-1997----------------Site C-------2
Lacy-2002------------------Site A-------3
Sumawinata-2003----------Site D-------2

I'm wondering if it's possible to have a function which looks in Count to see if there is more than one occurance of a study at that site, and if so list all the authors-years at that site, so it ends up looking something like:

Author-Year--------------------------------Site---------------Count
Sutanto-2009, Maguire-2006, Lacy-2002-----------Site A------------------3
Maguire-2006, Baird-1995--------------------------Site B-------------------2
Baird-1995, Fryauff-1997---------------------------Site C------------------2
Murphy-1993, Sumawinata-2003------------------Site D------------------2
Fryauff-1997----------------------------------------Site E-----------------1

Would anyone be able to help with a way to accomplish this? That'd be great!

Cheers