[R] function that uses a variable name as the parameter

[Duncan Murdoch]

On 12/11/2008 7:59 AM, David Croll wrote:
> 
> Hello dear R people!
> 
> 
> Several times it occurred to me that a function that uses a variable name as a parameter would be helpful, but I did not find out how to write such a function. I have experience in several programming language, but I did not come across a helpful trick...
> 
> What I want to have is...
> 
> a <- 12 # starting value
> 
> add <- function(variable,increment) {
> 
> variable <- variable + increment
> 
> }
> 
> # by typing a and 25 for example, you specify that 25 will be added to the variable a...
> 
> add(a,25)
> 
> # the new a equals 12 + 25 = 37
> 
> Thanks for all the help – I'll try to give my advice when I get across a problem I can solve!

That's not a good idea:  it looks as though you're trying to fake "call 
by reference" in a call by value language.  R is flexible enough to do 
it (use substitute() to change the arg into a string, get() to get the 
old value, assign() to put it back), but the behaviour will be really 
weird, and you'll probably run into problems later.  R is not C.

Duncan Murdoch