R recursive function to write hierarchical data frame to json file with childen

gistfile1.r

# http://stackoverflow.com/questions/12818864/how-to-write-to-json-with-children-from-r
# example input
# year month  size
# 2007     1   100
# ...
# 2007     12  850
# 2008      1  432
# ...

makeList <- function(x){
  if(ncol(x) > 2){
    listSplit <- split(x[-1], x[1], drop = T)
    lapply( names(listSplit),
            function(y){
              list(name = y, children = makeList(listSplit[[y]]))
              } )
  }
  else {
    lapply( seq(nrow(x[1])), 
            function(y){
              list(name = x[,1][y], size = x[,2][y])
            } )
  }
}

jsonStr <- toJSON(list(name="user",children=makeList(d2)))
fileConn<-file("data.json")
writeLines(jsonStr, fileConn)
close(fileConn)