[Rd] stringsAsFactors = FALSE

[hadley wickham]

On Mon, Nov 17, 2008 at 11:06 AM, William Dunlap <wdunlap at tibco.com> wrote:
>> From: r-devel-bounces at r-project.org
>> [mailto:r-devel-bounces at r-project.org] On Behalf Of hadley wickham
>> Sent: Monday, November 17, 2008 5:10 AM
>> To: r-devel at r-project.org
>> Subject: [Rd] stringsAsFactors = FALSE
>> ...
>> 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.
>
> I think expand.grid converts input strings to factors so they
> retain the order they have in the input.  (Note that the levels
> argument is unique(x), not the sort(unique(x)) that data.frame uses.)
> People generally give expand.grid sorted input and expect it to
> not alter the order (the order of the levels affects tables and
> and some plots).

Ah, that makes sense.  (Although the conversion to factors just seems
to be a convenient way to achieve the desired effect in this case -
there's no reason they have to be factors in the output)

Hadley

-- 
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