[R] meaning of lm( y~., data=mydat ), is it a language feature, is it documented, is it supported?

[peter dalgaard]

> On 23 May 2016, at 13:43 , Ivan Calandra <ivan.calandra at univ-reims.fr> wrote:
> 
> Hi John,
> 
> This is indeed documented, but you'll have to look at the function formula():
> ?formula
> 
> Regarding the dot (.), here is the explanation from the help of formula():
> "There are two special interpretations of . in a formula. The usual one is in the context of a data argument of model fitting functions and means ‘all columns not otherwise in the formula’: see terms.formula. In the context of update.formula, only, it means ‘what was previously in this part of the formula’."

Actually, it is debatable which one of those deserve to be called "usual". Once upon a time, in the heyday of John Tukey, it might have been usual to have data set of a few hundred rows and, like, a dozen columns, exactly one of which being the response. Not so much these days, I'd say.

-pd

> 
> HTH,
> Ivan
> 
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> 
> Le 23/05/2016 à 13:26, John Sorkin a écrit :
>>  The syntax
>> mydat <- data.frame( y,x )
>> fit1 <- lm( y~., data=mydat )
>> appears to perform a multivariable regression of y on every non-y variable in the data frame mydat. I can not find this syntax (y~.) in R documentation. Is y~. a supported feature of the R language? Where can I find it documented? I would hate to write code that is dependent on a non-supported, non-documented language feature.
>> Thank you,
>> John
>> John David Sorkin M.D., Ph.D.
>> Professor of Medicine
>> Chief, Biostatistics and Informatics
>> University of Maryland School of Medicine Division of Gerontology and Geriatric Medicine
>> Baltimore VA Medical Center
>> 10 North Greene Street
>> GRECC (BT/18/GR)
>> Baltimore, MD 21201-1524
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-- 
Peter Dalgaard, Professor,
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