文本分析，组间插入汇总值

【问题】

Ok, so I'm trying to read a log file and parse useful data out of it.
it looks kind of like
webcat_service,1.0,50
webcat_service,1.5,30
webcat_service,2.5,10
webcat_service,4.0,5
webroot_service,10.0,50
webroot_service,15.0,20
webroot_service,20.0,10
webroot_service,30.0,5
at this point.
Now, what I want is to split that off into 
webcat_service_1.0,50
webcat_service_1.5,30
webcat_service_2.5,10
webcat_service_4.0,5
webcat_service_avg, $FOO
webroot_service,10.0,50
webroot_service,15.0,20
webroot_service,20.0,10
webroot_service,30.0,5
webroot_service_avg, $BAR
I can do the easy part (putting the values together, running the function that spits back an average, and puts it in the right place), but I can't figure out how to write a loop that takes input until a variable is different, then put that into the check ("look at webcat until you