[R] getting data frame rows out of a by object

[Thomas Lumley]

On Thu, 8 Apr 2004, Ed L Cashin wrote:
>
> One thing I notice is that I get funny row names using this method.  I
> can change them back easily enough, though.
>

I think you can use interaction() rather than the factor(paste()) approach

interaction(d$a, d$b, drop=TRUE) gives a factor with one level for each
existing combination of d$a and d$b.

	-thomas