[R] counting frequencies across two columns

[Patrick Connolly]

On Sun, 01-Nov-2009 at 01:20AM -0500, Jason Priem wrote:

> 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

Let's call that dataframe x

>
> 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.  

I'm not clear what you require, but maybe it's this:

> with(x, table(articleID, author))

articleID andrews johnson jones smith
        1       0       0     1     0
        2       1       0     0     2
        3       0       1     1     0

Is that anything like what you're after?  


-- 
~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.~.   
   ___    Patrick Connolly   
 {~._.~}                   Great minds discuss ideas    
 _( Y )_  	         Average minds discuss events 
(:_~*~_:)                  Small minds discuss people  
 (_)-(_)  	                      ..... Eleanor Roosevelt
	  
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