[R] Function returning multiple objects but printing only one

[Duncan Murdoch]

On 13/07/2015 5:06 PM, Daniel Caro wrote:
> Hello,
> 
> Sorry if this has already been addressed before but I could not find any
> helpful references.
> 
> I would like to create a function that outputs a single element of a list
> but stores all elements, similar to  'lm' and many other functions. There
> are several answers on how to return multiple objects with lists, for
> example:
> 
> http://r.789695.n4.nabble.com/How-to-return-multiple-values-in-a-function-td858528.html
> 
> http://stackoverflow.com/questions/8936099/returning-multiple-objects-in-an-r-function
> 
> But the examples show how to print multiple outputs, such as
> 
> functionReturningTwoValues <- function() {return(list(first=1, second=2))}
> functionReturningTwoValues()
> 
> And I only want the function to print a single element from the list but
> still store the other elements such that they can be retrieved with
> functionReturningTwoValues$first, for example. My function produces
> bootstrap coefficients so clearly I don't want to print the bootstrap
> output but I do want users to be able to access it.

You need to give your object a class, and define a print method for that
class.  It's pretty simple:


functionReturningTwoValues <- function() {return(structure(list(first=1,
second=2), class="MyClass"))}

print.MyClass <- function(x, ...) {
  print(x$first, ...)
}

This is using "S3 classes".  There are other systems (S4, etc.) that let
you do this, but none are simpler.

Duncan Murdoch