[R] how to write assignment form of function

From: Heinz Tuechler <tuechler_at_gmx.at>
Date: Wed 10 Aug 2005 - 22:24:47 EST


Dear All,

where can I find information about how to write an assigment form of a function?
For curiosity I tried to write a different form of the levels()-function, since the original method for factor deletes all other attributes of a factor. Of course, the simple method would be to use instead of levels(x) <- newlevels, attr(x, 'levels') <- newlevels.

I tried the following:
## example
x <- factor(c(1,1,NA,2,3,4,4,4,1,2)); y <- x attr(x, 'levels') <- c('a', 'b', 'c', 'd') # does what I want x
 [1] a a <NA> b c d d d a b Levels: a b c d  

'levels.simple<-' <- function (x, value)  {

      attr(x, 'levels') <- value
 }  

levels.simple(y) <- c('a', 'b', 'c', 'd') # does not what I want y
[1] "a" "b" "c" "d"  

Thanks,
Heinz Tüchler



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