Hello all

I have a big data frame and I regularly want to break it down into subsets,
calculate some new data, and add it back to the data frame.

At the moment my technique seems a bit ugly and embarrassing. Something
like:

result <- by(mydata, mydata$some_factor, function (x) {
  # do something to create a vector v with length(v) == nrow(x)
 return(v)
})
# now result has a big list, argh... how do I put it neatly back into the
mydata data frame?
for (i in unique(mydata$some_factor) {
mydata$newvar[mydata$somefactor ==i] <- result[[i]]
}

What should I be doing instead of this?

David Hugh-Jones
Post-doctoral Researcher
Max Planck Institute of Economics, Jena
http://davidhughjones.googlepages.com

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