Passing and returning functions in R

Question

I want to create a function in R, which take data as a function, do some operation on it(add some columns/Rows etc) and return it. I found usually I can not do so.

f <- function(d = cars){
    d$new = ifelse(d$dist > rep(10, nrow(d)), 1, 0)
    return d 
}

Error: unexpected symbol in:
"d$new= ifelse(d$dist>rep(10,nrow(d)),1,0)
return d"

If I remove return d, I get only the vector, not whole data frame.
Any suggestion?

Please read: http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example — G. Grothendieck, Jun 09 '14 at 03:19
@Outlier, the first (accepted) answer tells you everything you need to know — Rich Scriven, Jun 09 '14 at 04:23
The key point is that should be possible for someone else to copy the code and data in your question and paste it into their session to reproduce your error on their end. — G. Grothendieck, Jun 09 '14 at 12:32

score 2 · Accepted Answer · answered Jun 09 '14 at 03:33

Functions in R return the value from the last statement executed. When you do an assignment, the value from the left side of the assignment is the (invisibly) returned result. For exampel

d <- cars
a <- (d$new <- ifelse(d$dist>10, 1, 0))
a

#  [1] 0 0 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
# [40] 1 1 1 1 1 1 1 1 1 1 1

So in your example you're merely returning the vector you just created. R doesn't know that you want to return the whole d data.frame. If you put the return(d), it will know that's what you want. You can even just put d on the last line by itself to return that value.

Great.. So my mistake was not adding parenthesis after return.. return(d) worked just fine. — Kuber, Jun 09 '14 at 03:42

Passing and returning functions in R

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