maybe try this:
| makeresults count=1
| eval data = "host1,a;host1,b;host2,c;host2,d;host3,a"
| makemv delim=";" data
| mvexpand data
| rex field=data "(?<project>[^,]+)\,(?<value>\S+)"
| table project value
| rename COMMENT as "the above creates data, below is the solution"
| streamstats count as number by project
hope it helps