Supress function output in R if argument missing

Question

I'm new to writing functions and would like to suppress the output if a given argument in a function is not reported without having to write multiple return() for each potential statement. For example:

fun <- function(x1,x2, y){
    if(missing(y)){result<- x1+x2}
    if(!missing(y)){ols<-lm(y ~ x1 + x2)}  
return(list(result = result, 
            ols = ols))

}   

x1 <- rnorm(100)
x2 <- rnorm(100)

fun(x1,x2)

When you run this, you get an error since the OLS isn't reported (if you include a y, you get the same problem for the object 'result'). Without including a specific return() function within each if statement, can you suppress one of the return elements? Thanks for any and all thoughts

Answer 1

You could use compact from plyr, in combination with initializing result and ols objects as NULL at the start.

library(plyr)

fun <- function(x1, x2, y){
  result = ols = NULL
  if(missing(y))
    result <- x1+x2
  if(!missing(y))
    ols <- lm(y ~ x1 + x2)
  return(compact(list(result = result, 
          ols = ols)))

}   

x1 <- rnorm(100)
x2 <- rnorm(100)

fun(x1,x2)

plyr::compact removes NULL elements from a list