r - Accesing a variable in a ggplot function

Question

I have a sample data below

data <- data.frame(yr=c(1999,2000,2001,2002,2003,2004,2005,2006,2007,2009,2010,2011,2012), 
                   ntemp =c(11,12,13,14,15,16,17,18,19,20,21,12,23))

When I try running this function, to access the variable inside a ggplot function.

FUN<-function(data, fun.y,yr) {
  fun.data <- data     
  ggplot(fun.data,aes(yr, fun.y))+geom_point()+scale_y_continuous(fun.y)    
}

FUN(data, "ntemp", yr)

I get an Error in eval(expr, envir, enclos) : object 'fun.y' not found

How can I solve this on R3.02?

Answer 1

aes only looks at the variables in data argument. If you would like to pass variable as an argument to FUN by its character name, use aes_string:

FUN <- function(data, x, y) {
  ggplot(data, aes_string(x=x, y=y)) + geom_point()
}

FUN(data, y="ntemp", x="yr")

A small correction: variable inside aes call should be defined in the scope where the ggplot object is evaluated, so technically a variable is looked up in data first, then in global environment (by default). See this and this questions.