[R] re-coding variables

[Peter Dalgaard]

Marc Bernard <bernarduse1 at yahoo.fr> writes:

> Dear All,
>    
>   I wonder how to re-code  a categorical variable without using the ifelse loops. For example:

(What's an "ifelse loop"???)

>   Let X be a categorical variable with 6 levels, levels(X) = c(1,2,3,4,5,6)
>    
>   How to create a new categorical variable Y with levels, 10,11,12, say , such that:
>   Y = 10 if X =1 or X=2
>   Y = 11 if X =3 or 4
>   Y =11 if X = 5 or 6

One way is the recode() function in the car package. Another is 

Y <- X
levels(Y) <- c(10,10,11,11,12,12)

or 

levels(Y) <- list("10"=c(1,2),"11"=c(3,4),"12"=c(5,6))

and a 4th one could be

Y <- factor(c(10,10,11,11,12,12)[X])

(which may need a safeguarding "levels=c(10,11,12)" in case not all
levels are present).
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