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Define return values of a function

4 messages · Soeren.Vogel at eawag.ch, Baptiste Auguie, David Winsemius +1 more

Soeren.Vogel at eawag.ch
# 
I have created a function to do something:

i <- factor(sample(c("A", "B", "C", NA), 793, rep=T, prob=c(8, 7, 5,  
1)))
k <- factor(sample(c("X", "Y", "Z", NA), 793, rep=T, prob=c(12, 7, 9,  
1)))
mytable <- function(x){
   xtb <- x
   btx <- x
   # do more with x, not relevant here
   cat("The table has been created, see here:\n")
   print(xtb)
   list(table=xtb, elbat=btx)
}
tbl <- table(i, k)
mytable(tbl) # (1)
z <- mytable(tbl) # (2)
str(z) # (3)

(1) Wanted: outputs the string and the table properly. *Unwanted*:  
outputs the list elements.

(2) and (3) Wanted: outputs the string properly. Wanted: assigns the  
list properly.

How can I get rid of the *unwanted* part? That is, how do I define  
what the functions prints and -- on the other hand -- what it returns  
without printing?

Thanks

S?ren
Baptiste Auguie
# 
hi,

Try making your last line

 invisible( list(table=xtb, elbat=btx) )


HTH,

baptiste

2009/11/22 Soeren.Vogel <Soeren.Vogel at eawag.ch>:
David Winsemius
#
On Nov 22, 2009, at 6:26 AM, soeren.vogel at eawag.ch wrote:

            

      
      
      
    

        
Whet the author of a function wants a particular object that exists  
insode a function to be returned they may warp it in the function  
return(). Otherwise R returns the result of the last evaluation which  
in this case was list(table=xtb, elbat=btx).

If you want the function to return <something else>. then you could   
put <something else> last in the sequence. If you want it to return  
<nothing> than put this at the end:

return()

If you want the results to not be printed the use invisible()

Perhaps:
  invisible(list( elbat=btx))   #substituted for list(table=xtb,  
elbat=btx) after the print line

 > tbl <- table(i, k)
 > mytable(tbl) # (1)
The table has been created, see here:
    k
i     X   Y   Z
   A 119  69  89
   B 116  70  97
   C  80  36  52
 > z <- mytable(tbl) # (2)
The table has been created, see here:
    k
i     X   Y   Z
   A 119  69  89
   B 116  70  97
   C  80  36  52
 > str(z) # (3)
List of 1
  $ elbat: 'table' int [1:3, 1:3] 119 116 80 69 70 36 89 97 52
   ..- attr(*, "dimnames")=List of 2
   .. ..$ i: chr [1:3] "A" "B" "C"
   .. ..$ k: chr [1:3] "X" "Y" "Z"

            

      
      
      
    

        
If you want to return the list, elbat, then just put the name of the  
list last in your case inside invisible or put it inside return().

            

      
      
      
    

        
That set by cat and print in your case.

            

      
      
      
    

        
By return()  or the order of evaluation

            

      
      
      
    

        
--

David Winsemius, MD
Heritage Laboratories
West Hartford, CT

  
  


  


      

    

    
1 day later

    

      
      

        


  

        

      Greg Snow
    

    

      
      #
    

  


  

      
If you want to control what gets printed in the output of your function, then you need to get into creating classes and methods.  Choose a class to return from your function, and create a print method for that class, then when you run your function the output will cause the print method to be called if you don't store the object, but the entire object will be available if stored.  E.g.:

testfunc <- function(x) {
	out <- list( a=summary(x), b=quantile(x), c=range(x) )
	class(out) <- 'myclass'
	return(out)
}

print.myclass <- function(x) {
	cat('my output:\n')
	print(x$a)
	cat('\n\n')
	cat('Q1: ',x$b[2], '\n')
	return(invisible(x))
}

testfunc(rnorm(100))
tmp <- testfunc(rnorm(100))
tmp
str(tmp)

Hope this helps,