[R] period in scale parameter of prcomp

[Greg Hirson]

Bill,

Thanks. So it is as we suspected.

Kind regards,
Greg

On 5/13/11 11:19 AM, William Dunlap wrote:
>> -----Original Message-----
>> From: r-help-bounces at r-project.org 
>> [mailto:r-help-bounces at r-project.org] On Behalf Of Greg Hirson
>> Sent: Friday, May 13, 2011 10:58 AM
>> To: R-help at r-project.org
>> Subject: [R] period in scale parameter of prcomp
>>
>> Hi all,
>>
>> Looking at the help file for prcomp and the code in
>> stats:::prcomp.default, the scale parameter for the default S3 method
>> has a trailing period: it written as
>>
>> scale.
>>
>> I assume there is a reason for it (backwards compatibility with S was
>> suggested) but I thought I'd ask.
> In ancient versions of S you would get an error running
> a function like
>    f <- function(x, plot=TRUE) { if (plot) plot(x, x^2) }
> because when it evaluated plot(x,x^2) the object called
> 'plot' was a logical vector, not a function.  The usual
> workaround was to call the argument 'plot.', as in
>    f <- function(x, plot.=TRUE) { if (plot.) plot(x, x^2) }
> You could still call it as
>    f(x, plot=FALSE)
> since tag abbreviations are allowed in function calls.
>
> Now the 'plot' in the function call 'plot(x,x^2)' is looked
> up differently than the 'plot' in 'if(plot)': the former
> search keeps going until it finds a function object.  Hence
> the dot is no longer needed, although it might make you think
> about how 'plot' can mean two different things in the same
> environment.  Older functions still have this dot because
> there is no good reason to change them and changing them can
> break old code.
>
> Bill Dunlap
> Spotfire, TIBCO Software
> wdunlap tibco.com  
>
>> Thanks,
>> Greg
>>
>> -- 
>> Greg Hirson
>> ghirson at ucdavis.edu
>>
>> Graduate Student
>> Agricultural and Environmental Chemistry
>>
>> 1106 Robert Mondavi Institute North
>> One Shields Avenue
>> Davis, CA 95616
>>
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-- 
Greg Hirson
ghirson at ucdavis.edu

Graduate Student
Agricultural and Environmental Chemistry

1106 Robert Mondavi Institute North
One Shields Avenue
Davis, CA 95616