R: ggplot_build is included in function

Question

I will try to run the ggplot_build inside a function and it returns the error: Error in eval(expr, envir, enclos) : object 'myData' not found Here is the code:

   # Summarise number of movie ratings by year of movie
mry <- do.call(rbind, by(movies, round(movies$rating), function(df) {
  nums <- tapply(df$length, df$year, length)
  data.frame(rating=round(df$rating[1]), year = as.numeric(names(nums)), number=as.vector(nums))
}))

p <- ggplot(mry, aes(x=year, y=number, group=rating))
p + geom_line()

function_mm <- function(myData){
    for(j in 1:2){ 
      p1 <- ggplot(myData, aes(x=myData[,2], y=myData[,3])) + geom_line()
      g1 <- ggplot_gtable(ggplot_build(p1))
    }
  return(p1)
}
Q1 <- function_mm(mry)

The code is running correctly when it is outside a function:

for(j in 1:2){ 
          p1 <- ggplot(myData, aes(x=myData[,2], y=myData[,3])) + geom_line()
          g1 <- ggplot_gtable(ggplot_build(p1))
        }

Thanks in advance!

Roland Roland · Accepted Answer · 2015-11-09T17:23:48

You made the classic mistake of using aes (with its non-standard evaluation) when you should use aes_string:

function_mm <- function(myData){
  for(j in 1:2){ 
    xy <- names(myData)[c(2, 3)]
    p1 <- ggplot(myData, aes_string(x=xy[1], y=xy[2])) + geom_line()
    g1 <- ggplot_gtable(ggplot_build(p1))
  }
  return(p1)
}
Q1 <- function_mm(mry) 
#works

R: ggplot_build is included in function

1 Answers