From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>

Date: Thu 11 Aug 2005 - 00:18:33 EST

Date: Thu 11 Aug 2005 - 00:18:33 EST

On Wed, 10 Aug 2005, Heinz Tuechler wrote:

> where can I find information about how to write an assigment form of a

*> function?
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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.
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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
**> }
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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"
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-- Brian D. Ripley, ripley@stats.ox.ac.uk 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 ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.htmlReceived on Thu Aug 11 00:25:14 2005

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