modify variable within R function

Question

How do I modify an argument being passed to a function in R? In C++ this would be pass by reference.

g=4
abc <- function(x) {x<-5}
abc(g)

I would like g to be set to 5.

Answer 1

There are ways as @Dason showed, but really - you shouldn't!

The whole paradigm of R is to "pass by value". @Rory just posted the normal way to handle it - just return the modified value...

Environments are typically the only objects that can be passed by reference in R.

But lately new objects called reference classes have been added to R (they use environments). They can modify their values (but in a controlled way). You might want to look into using them if you really feel the need...

Answer 2

There has got to be a better way to do this but...

abc <- function(x){eval(parse(text = paste(substitute(x), "<<- 5")))}
g <- 4
abc(g)
g

gives the output

[1] 5