[R] pass lm( ) a char vector as the variables to be included

[Emmanuel Charpentier]

Gavin Simpson a écrit :
> On Mon, 2007-11-26 at 14:17 +0000, Richard.Cotton at hsl.gov.uk wrote:
>>> Here are the codes of the example of lm( ):
>>>
>>> ## Annette Dobson (1990) "An Introduction to
>>> Generalized Linear Models".
>>> ## Page 9: Plant Weight Data.
>>> ctl <-
>>> (4.17,5.58,5.18,6.11,4.50,4.61,5.17,4.53,5.33,5.14)
>>> trt <-
>>> (4.81,4.17,4.41,3.59,5.87,3.83,6.03,4.89,4.32,4.69)
>>> group <- gl(2,10,20, labels=c("Ctl","Trt"))
>>> weight <- c(ctl, trt)
>>> anova(lm.D9 <- lm(weight ~ group))
>>> lm.D90 <- lm(weight ~ group - 1) # omitting intercept
>>>
>>> What I am doing is let the variable name "group"
>>> stored in a vector, say, g <- "group". The question is
>>> how to strip the quotation marks when we call lm( )
>>> through g?
>> Try: 
>> w = "weight"
>> g = "group"
>> form = as.formula(paste(w,g,sep="~"))
>> lm(form)
>>
>> Regards,
>> Richie.
> 
> For more complicated automation, the ideas and examples from Bill
> Venables Programmer Niche article in the R newsletter from a few years
> ago might be of use:
> 
> [39] Bill Venables. Programmer's niche. R News, 2(2):24-26, June 2002.
> [ bib | PDF | http ]
> 
> The PDF is available here:
> 
> http://cran.r-project.org/doc/Rnews/Rnews_2002-2.pdf

Another possibility is to create macro (library(gtools) ; ? defmacro).
See Thomas Lumley's paper in R News 2001-3 ("Programmer’s Niche: Macros
in R\n Overcoming R’s virtues).

HTH,

					Emmanuel Charpentier