[R] Simple summary question

[Andrew Perrin]

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

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Andrew J Perrin - andrew_perrin at unc.edu - http://www.unc.edu/~aperrin
 Assistant Professor of Sociology, U of North Carolina, Chapel Hill
      269 Hamilton Hall, CB#3210, Chapel Hill, NC 27599-3210 USA


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