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

From: ivo welch <ivowel_at_gmail.com>
Date: Mon, 21 Mar 2011 18:42:43 -0400


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



Ivo Welch (ivo.welch_at_brown.edu, ivo.welch_at_gmail.com)

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