[R] Referencing factors through their equivalent numeric level

[Berend Hasselman]

On 02-05-2012, at 07:22, Kaushik Krishnan wrote:

> Hey folks
> 
> I'm sorry for bringing what must be a very simple question to R-help,
> but after some research I haven't been able to find a solution to my
> problem.
> 
> Suppose I create a simple factor:
> [code]
>> x<-c("A","B","B","C","A")
>> x
> [1] "A" "B" "B" "C" "A"
>> x <- as.factor(x)
>> x
> [1] A B B C A
> Levels: A B C
> [/code]
> 
> Now, when I see this factor in terms of its numeric level values, I get
> [code]
>> as.numeric(x)
> [1] 1 2 2 3 1
> [/code]
> 
> Suppose I have
> [code]
> y <- 2
> [/code]
> 
> I want the numeric value of y to reference the level of factor x. That
> is, I am looking for a function (`foo') so that I will get the
> following
> [code]
> foo(y) #or maybe foo(y,x)
> [1] B
> [/code]
> 
> I can think of a roundabout way of doing through a user defined
> function, but I am sure that there is a built-in function that offers
> this functionality. I'd be grateful if someone could tell me what that
> function is.

Maybe this?

levels(x)[y]

Berend