[R] Merging by() results back into original data frame?

[ivo welch]

dear R experts---I am trying to figure out what the recommended way is
to merge by() results back into the original data frame.  for example,
I want to have a flag that tells me whether a particular row contains
the maximum for its group.

  d <- data.frame(group=as.factor(rep(1:3,each=3)), val=rnorm(9))
  highestvals <- by( d, d$group, function(d)(max(d$val)) )

  ## and now?  iterate over levels( d$group ) ?  how do I merge
highestvals back into d?

advice appreciated.

sincerely,

/iaw
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Ivo Welch (ivo.welch at brown.edu, ivo.welch at gmail.com)