ggplot2 not recognising column names in function

Question

My goal is to have a function in which can input specific column and df names, in order to output graphs in a consistent format. However, I am having some trouble with creating functions using ggplot2, because of problems with column name recognition. So far, I haven't had any success with any of the fixes people have proposed in other questions addressing this issue.

Using a test dataset as an example, this is what I tried first

set.seed(123)

MYdata1 <- data.frame(Time = 1:1000,
                    Zscore = rnorm(1000))

plot_testassess <- function(data1,xvar = "Time",yvar = "Zscore"
){ggplot(data = data1, aes(.data[[xvar]], .data[[yvar]]))}

plot_testassess(MYdata1,Time,Zscore)

However, I kept getting the error

Error in enquo(x) : object 'Time' not found

so then I tried aes_string, like this :

plot_testassess <- function(data1,xvar = "Time",yvar = "Zscore"
){ggplot(data = data1, aes_string(x=xvar,y=yvar))}

plot_testassess(MYdata1,Time,Zscore)

But in this case I got the following error.

Error in aes_string(x = xvar, y = yvar) : object 'Time' not found

I am at a loss as to how to make ggplot2 recognise that my column variables are not objects. Does anyone have any thoughts?

Ahhhh thank you !!! I've trawled hundreds of questions but didn't come across this one, I have no idea why!! — Liptongal, Jul 10 '23 at 16:49
Call your functions with strings `plot_testassess(MYdata1,"Time","Zscore")` — MrFlick, Jul 10 '23 at 16:50

score 2 · Accepted Answer · answered Jul 10 '23 at 16:56

library(ggplot2)

set.seed(123)
MYdata1 <- data.frame(Time = 1:1000,
                      Zscore = rnorm(1000))

You can make your function work, by putting quotation marks around the variable names in the function call. (I added geom_line() to you function so we get a visible result; nothing else is changed here.)

plot_testassess <-
  function(data1,
           xvar = "Time",
           yvar = "Zscore") {
    ggplot(data = data1, aes(.data[[xvar]], .data[[yvar]])) +
      geom_line()
  }

plot_testassess(MYdata1, "Time", "Zscore")

If you prefer to be able to provide the variable names without quotation marks you can drop the .data[[]] and embrace xvar and yvar with {{}}.

plot_testassess_nse <-
  function(data1,
           xvar = "Time",
           yvar = "Zscore") {
    ggplot(data = data1, aes(
        {{xvar}}, 
        {{yvar}}
      )) +
      geom_line()
  }

plot_testassess_nse(MYdata1, Time, Zscore)

Thanks! I really like the brace alternative! – Liptongal Jul 12 '23 at 15:42 — Liptongal, Jul 12 '23 at 15:42

ggplot2 not recognising column names in function

1 Answers1