[Rd] stringsAsFactors = FALSE

[Prof Brian Ripley]

On Mon, 17 Nov 2008, Prof Brian Ripley wrote:

> On Mon, 17 Nov 2008, hadley wickham wrote:
>
>> Hi all,
>> 
>> I love the option to not automatically convert strings into factors,
>> but there are three places that the current option doesn't work where
>> I think it should:
>
> Perhaps you mean 'when I would like it to'?   Things *should* work as 
> documented, surely?
>
>> options(stringsAsFactors = FALSE)
>> 
>> str(expand.grid(letters))
>> str(type.convert(letters))
>> 
>> df <- read.fwf(textConnection(paste(letters,collapse="\n")), 1)
>> str(df)
>
> I get
>
>> str(df)
> 'data.frame':   26 obs. of  1 variable:
> $ V1: chr  "a" "b" "c" "d" ...
>
> so what is wrong with that?  read.fwf just calls read.table, so the default 
> options of read.table apply.
>
>> I think type.convert and read.fwf can be fixed by giving them a
>> stringsAsFactors argument and then using asis = !stringsAsFactors
>> (like read.table).
>
> Seems to me that there is nothing wrong with read.fwf.  For type.convert() we 
> could have the default
>
> as.is = !default.stringsAsFactors()
>
> but I think a strong case needs to be made to change the documented 
> behaviour.

It seems only to be used in RODBC (where I have some extra control 
pending), simecol and BioC:beadarraySNP (both with as.is=TRUE) and reshape 
(author, one Hadley Wickham).  Given it is documented as a help utilty, it 
seems up to the caller to set the behaviour he wants.

>
>>  The key lines in expand.grid would seem to be
>>
>>            if (!is.factor(x) && is.character(x))
>>                x <- factor(x, levels = unique(x))
>> 
>> but I'm not sure why they are being converted to factors in the first 
>> place.
>
> Nor I am, but it goes back to at least r2107, over 10 years ago.  I don't see 
> much problem with adding a 'stringsAsFactors' argument there.
>
> -- 
> Brian D. Ripley,                  ripley at 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
>
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>

-- 
Brian D. Ripley,                  ripley at 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