R help - Nov 2007 - pass lm( ) a char vector as the variables to be included

Dear Everyone in list:
I am writing some codes to automate the process of
fitting linear models where the names of variables of
models are produced and stored in character vectors.
But I have problems to pass the vectors to the lm( )
because I don't know how to strip the quotation marks
automatically. 

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?

Thank you all.

Boshao



     
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> 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.

Mathematical Sciences Unit
HSL


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