I've got a data frame describing comments on an electronic journal,
wherein each row is a unique comment, like so:
commentID author articleID
1 1 smith 2
2 2 jones 3
3 3 andrews 2
4 4 jones 1
5 5 johnson 3
6 6 smith 2
I want know the number of unique authors per article. I can get a table
of article frequencies with table(articleID), but I can't figure out how
to count frequencies in a different column. I'm sure there's an easy
way, but I guess I'm too new at this to find it. Thanks for your help!
Jason Priem
PhD student, School of Information and Library Science, University of
North Carolina-Chapel Hill
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