[R] Simple summary question

[A.J. Rossini]

>>>>> "AP" == Andrew Perrin <andrew_perrin at unc.edu> writes:

    AP> I'd like to get summary statistics (really just a mean would
    AP> be fine) for a vector in a data frame, but split based on the
    AP> value of another vector.  That is, I have a data frame
    AP> (hcd.df) with variables datecat (which is always 1 or 2) and
    AP> auth.sum (-8..+8).  I've used xtabs to get chi-square
    AP> comparisons, but what I need now is a simple mean of auth.sum
    AP> where datecat is 1 and another where datecat is 2. Thanks for
    AP> any advice.

Something like :

        lapply(split(hcd.df$auth.sum,hcd.df$datecat),mean)

?


-- 
A.J. Rossini				Rsrch. Asst. Prof. of Biostatistics
U. of Washington Biostatistics		rossini at u.washington.edu	
FHCRC/SCHARP/HIV Vaccine Trials Net	rossini at scharp.org
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