CODEWITHSUNDEEP
r
Carlos David
Carlos David

Reputation: 73

Hiding a result of a function in R

I created a function that has four output arguments, for example:

myfuction<-function(...){     
    #Inside the function I created four results A, B, C, and D.    
    A = ...    
    B = ...    
    C = ...    
    D = ...     
    z<-list(MacKinnon=A,regression=B,proof=C, res=D)    
    return(z)
}

The result D corresponds to a vector of numbers that respresents the residuals of a regression.

My question is How can I hide this result without removing it? That is, I want that when I run the function, the results A, B, and C appear, but not the result D.

And if I want to access the result D, I have to do something like this:

X <-myfuction (...)
X$res

to be able to observe the residual.

Upvotes: 7

Views: 625

Answers (2)

csgillespie
csgillespie

Reputation: 60522

I would just use an S3 class. Basically, just tag the object z with a particular class

myfunction <- function(){     
  #Inside the function I created four results A, B, C, and D.    
  A = 10;B = 20;C = 30; D = 40     
  z = list(MacKinnon=A, regression=B, proof=C, res=D)    
  class(z) = "my_fun" # Tagging here
  return(z)
}

Create an S3 print function for my_fun

print.my_fun = function(x, ...) print(x[1:3])

Then

R> x = myfunction()
R> x
$MacKinnon
[1] 10

$regression
[1] 20

$proof
[1] 30

But 

R> x$res
[1] 40

gives you want you want.

A couple of comments/pointers.

  • Typically when you assign the class, you would use something like 

    class(z) = c("my_fun", class(z))

    however, since we just created z in the line above, this isn't needed.

  • Currently the print method strips away any additional classes (in the example, there is only one class, so it's not a problem). If we wanted to maintain multiple class, we would use

    print.my_fun = function(x, ...) {
  x = structure(x[1:3], class = class(x)) 
  NextMethod("print")
}

    The first line of the function subsets x, but maintains all other classes. The second line, then passes x to the next print.class_name function.

Upvotes: 10

Gabe
Gabe

Reputation: 649

You can use invisible.

For example, this would print nothing to the console but allow you to assign it's output:

myfunction<-function(){
    #Inside the function I created four results A, B, C, and D.
    A = 1; B = 2; C = 3; D = 4
    z<-list(MacKinnon=A,regression=B,proof=C, res=D)
    return(invisible(z))
}

myfunction()       # nothing prints
x <- myfunction()
x                  # now it does!
# $MacKinnon
# [1] 1

# $regression
# [1] 2

# $proof
# [1] 3

# $res
# [1] 4

If you want specific parts printed to the console, you can use print or cat for those.

myfunction<-function(){
    #Inside the function I created four results A, B, C, and D.
    A = 1;    B = 2;    C = 3;    D = 4
    z<-list(MacKinnon=A,regression=B,proof=C, res=D)
    print(A)
    return(invisible(z))
}

myfunction()
# [1] 1

This is useful if you don't want the output to be printed when the function runs without being assigned. If you don't want it to print after it's been assigned to a variable, then you should create a print method like @csgillespie suggested.

Upvotes: 0

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