[R] Trying to learn how to write a function... can't define a variable??

[Rui Barradas]

Hello,

Start by (re-)reading An Introduction to R, file R-intro.pdf in your doc 
directory. Chapter 10.

You're just computing, not returning the result of that computation. Nor 
anything else, ADD() does not return a value. (See the example in 
R-intro, section 10.1)
And you need to assign the return value to change the value of 'z' 
_outside_ the function. R passes arguments by value, what happens inside 
functions stays inside functions. (R-intro, section 10.5, first sentence.)

# Right way
z <- 1
ADD <- function(x){
     x <- x + 1
     x
}
ADD(z)  # returns 2
z  # still 1
z2 <- ADD(z)
z2  # equals 2

Hope this helps,

Rui Barradas
Em 07-09-2012 19:00, wwreith escreveu:
> I am just starting to experiment with writing a function and have run into
> what seems like a limitation or more likely a lack of understanding on my
> part.
>
> Very Simple Example:  I want to define a function that does 1+1=2.
>
> z<-1
> ADD<-function(x)
> {
> x<-x+1
> }
> ADD(z)
> z
>   output for z is 1 not the expected 2.
>
> Now if I were to do print(x+1) instead of x<-x+1 it does return 2, so the
> function seems ok with x+1, but not ok with x<-. Is there a way to define a
> variable inside a function or am I violating some rule that I don't know
> about?
>
> Thanks for the help!
>
> Will
>
>   
>
>
>
> --
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>
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