Question

I would like to write a function that creates a plot of a set of numbers and adds a regression line. As of now, I can still create the plot but I either get an error with the plot, or some sort of Null response.

My function without a regression line that returns no null looks like this:

fun<-function(){
+   x<-c(1,2,3,4,5)
+   y<-c(1,2,3,4,5)
+   LR<-lm(x~y)
+   
+   return(plot(x,y))
+ }
> fun()

Nice and Pretty with just a plot as a result

if I add the regression line to the plot, I still get the plot but I also get a null response

> fun<-function(){
+   x<-c(1,2,3,4,5)
+   y<-c(1,2,3,4,5)
+   LR<-lm(x~y)
+   p<-plot(x,y)
+   a<-abline(LR)
+   return(p)
+ }
> fun()
NULL

or an error

> fun<-function(){
+   x<-c(1,2,3,4,5)
+   y<-c(1,2,3,4,5)
+   
+   LR<-lm(x~y)
+   
+   p<-plot(x,y)
+   a<-abline(LR)
+   
+   return(p,a)
+ }
> fun()
Error in return(p, a) : multi-argument returns are not permitted

or two nulls

> fun<-function(){
+   x<-c(1,2,3,4,5)
+   y<-c(1,2,3,4,5)
+   
+   LR<-lm(x~y)
+   
+   p<-plot(x,y)
+   a<-abline(LR)
+   
+   return(list(p,a))
+ }
> fun()
[[1]]
NULL

[[2]]
NULL

Sorry if this seems ridiculously nit picky, but in the actual data set it can get ugly.

Answer 1

Does this do what you want?

fun <- function(x, y) {
  plot(x, y)
  abline(lm(x~y))
}

fun(1:10, 10:1)

If you’re hoping for a plot object to return for further manipulation, you can use ggplot:

fun <- function(df) {
  ggplot(df, aes(X, y)) + geom_point()
}

df <- data.frame(x=1:10, y=10:1)
p <- fun(df)

# examine p
str(p)

# plot p
p