What ways are there to edit a function in R?

Question

Let's say we have the following function:

foo <- function(x) {     line1 <- x     line2 <- 0     line3 <- line1 + line2     return(line3) } 

And that we want to change the second line to be:

    line2 <- 2 

How would you do that?

One way is to use

fix(foo) 

And change the function.

Another way is to just write the function again.

Is there another way? (Remember, the task was to change just the second line)

What I would like is for some way to represent the function as a vector of strings (well, characters), then change one of it's values, and then turn it into a function again.

Answer 1

There is a body<- function that lets you assign new content of the function.

body(foo)[[3]] <- substitute(line2 <- 2) foo #-----------     function (x)  {     line1 <- x     line2 <- 2     line3 <- line1 + line2     return(line3) } 

(The "{" is body(foo)[[1]] and each line is a successive element of the list. Therefore the second line is the third element in the expression list. The inserted elements need to be unevaluated expressions rather than text.)

There is also a corresponding formals<- function that lets one perform similar surgery on the argument pairlist.

Note: fixInNamespace is probably a better choice than fix if the function will be calling accessory functional resources in a loaded package. When used from the console, both fix will assign results to the .GlobalEnv.