[R] tapply and more than one function, with different arguments

[Peter Ehlers]

Try replacing 'max' with 'mean' and see what you get.
Then have a look at ?max and see what max() does with
extra arguments.

I'm not sure it's relevant, but it might be useful
to check what Hmisc::summarize does.

  -Peter Ehlers

RINNER Heinrich wrote:
> Dear R-users,
> 
> I am working with R version 2.10.1.
> 
> Say I have is a simple function like this:
> 
>> my.fun <- function(x, mult) mult*sum(x)
> 
> Now, I want to apply this function along with some other (say 'max') to a simple data.frame, like:
> 
>> dat <- data.frame(x = 1:4, grp = c("a","a","b","b"))
> 
> Ideally, the result would look something like this (if mult = 10):
>   max my.fun
> a   2     30
> b   4     70
> 
> I have tried it that way:
> 
> apply.more.functions <- function(dat, FUN = c("max", "my.fun"), ...) {
>   res <- NULL
>   for(f in FUN) res[[f]] <- tapply(dat$x, dat$grp, FUN = f, ...)
>   data.frame(res)
> }
> 
> # let's test it:
>> apply.more.functions(dat, FUN = c("max", "min"))
>   max min
> a   2   1
> b   4   3
> # perfect!
> 
> # now, with an additional argument:
>> apply.more.functions(dat, FUN = c("max", "my.fun"), mult = 10)
>   max my.fun
> a  10     30
> b  10     70
> # uhuh!
> Apparently, 'mult' has been used in the calculation of 'max' as well.
> How can I modify apply.more.functions in order to avoid this?
> 
> Your advice would be appreciated;
> Kind regards
> Heinrich.
> 
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> 
> 

-- 
Peter Ehlers
University of Calgary