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rggplot2facet-grid

R: "Error in facet_grid" - "unused argument"

I am trying to plot some data from my experiment in R using ggplot2, and I am trying to split the graph in two parts using facet_grid().

Here is an MWE I built with the cars dataset:

data(mtcars)
ggplot(data=mtcars, aes(x=mtcars$mpg,y=mtcars$cyl)) + 
  geom_point()+
  facet_grid(rows=mtcars$disp)

I get the following error:

Error in facet_grid(rows = mtcars$disp) : 
  unused argument (rows = mtcars$disp)

I really have no idea why this is happening. I used this function before, and it worked fine. Would appreciate ideas on how to solve this.

edit: I accepted the second answer, because it provides some more context, but as I see it, both are equally correct in pointing out that I need to quote the variable name. The actual error was resolved after installig R and all packages again. Now I have a new error, but that is another story. Thanks again!

Solution

  • First, don't explicitly refer to mtcars within the aes() call. Second, quote the facet argument.

    library(ggplot2)    
ggplot(data=mtcars, aes(x=mpg,y=cyl)) + 
  geom_point()+
  facet_grid(rows="disp")

    Also, consider creating a new variable that collapses disp into fewer values for the facet to be more meaningful & readable.

    not-cut

    Here's an example of four arbitrary cut points.

    mtcars$disp_cut_4 <- cut(mtcars$disp, breaks=c(0, 200, 300, 400, 500))
ggplot(data=mtcars, aes(x=mpg,y=cyl)) + 
  geom_point()+
  facet_grid(rows="disp_cut_4")

    cut