Question

I’m trying to make a function using ddply inside of it. However I can’t get to work. This is a dummy example reproducing what I get. Does this have anything to do this bug?

library(ggplot2)
data(diamonds)

foo <- function(data, fac1, fac2, bar) {
  res <- ddply(data, .(fac1, fac2), mean(bar))
  res
}

foo(diamonds, "color", "cut", "price")

Answer 1

I don’t believe this is a bug. ddply expects the name of a function, which you haven’t really supplied with mean(bar). You need to write a complete function that calculates the mean you’d like:

foo <- function(data, fac1, fac2, bar) {
  res <- ddply(data, c(fac1, fac2), function(x,ind){
                                     mean(x[,ind]},bar)
  res
}

Also, you shouldn’t pass strings to .(), so I changed that to c(), so that you can pass the function arguments directly to ddply.