On Wed, 10 Aug 2005, Heinz Tuechler wrote:
> where can I find information about how to write an assigment form of a
> function?
In all good books on S programming, or by studying examples. But in this
case the problem is actually about defining functions with the return
value you expect.
> 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.
And that would not do what the current function does, which is to merge
levels as required.
I suggest you look at levels<-.factor in R-devel, which does not drop
attributes.
> 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
> }
This did not return anything! Try returning 'x'.
> levels.simple(y) <- c('a', 'b', 'c', 'd') # does not what I want
> y
> [1] "a" "b" "c" "d"
--
Brian D. Ripley, [EMAIL PROTECTED]
Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
University of Oxford, Tel: +44 1865 272861 (self)
1 South Parks Road, +44 1865 272866 (PA)
Oxford OX1 3TG, UK Fax: +44 1865 272595
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