[R] understanding the FUNCTION function

[Rui Barradas]

Hello,

>
> gives you 120, but you cannot access it after the end of execution. 
>

Because you're just printing the final value of 'a', not returning it.

fac <- function(x){
	a <- 1
	for(i in 1:x) a <- a*i
	a
}

The return value must be the last instruction in a function.
Then, if you want, you can assign it to a variable that exists in the
environment the function was called from.
This is the usual practice, and it makes sense. Once a function is written
you don't have to worry with what
happens inside it. The caller's environment, it's variables, should not be
changed.
That's why '<<-' is not recommended. You might have variables with surprise
values.
Read, like said earlier, the R Inferno, Circle 6:

    "What's so wrong about global assignments? Surprise.
    Surprise in movies and novels is good. Surprise in computer code is
bad."

And download it.

http://www.burns-stat.com/pages/Tutor/R_inferno.pdf

Rui Barradas


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