renaming the output column with the plyr package in R

Question

Hadley turned me on to the plyr package and I find myself using it all the time to do \'group by\' sort of stuff. But I find myself having to always rename the resulting col

Answer 1

This seems to work:

> groupAcres <- ddply(mydata, c("state"), function(df) c(myName=sum(df$acres)))
> groupAcres
  state   myName
1     A 56.87973
2     B 57.84451
3     C 52.82415

Answer 2

Use summarise (or summarize):

  groupAcres <- ddply(mydata, "state", summarise, 
     myName = sum(acres))