[R] lm with an arbitrary number of terms

[Peter Dalgaard BSA]

Richard Nixon <richard.nixon at mrc-bsu.cam.ac.uk> writes:

> Hello folks,
> 
> Any ideas how to do this?
> 
> data.frame is a data frame with column names "x1",...,"xn"
> y is a response variable of length dim(data.frame)[1]
> 
> I want to write a function
> 
> function(y, data.frame){
>     lm(y~x1+...+xn)
> }
> 
> This would be easy if n was always the same.
> If n is arbitrary how could I feed the x1+...+xn terms into lm(response~terms)?
> 

You could build up the formula in a for loop; something like

n <- names(my.data.frame)
f <- as.symbol(n[1])
for (i in 2:length(n))
  f <- substitute(f+a,list(a=as.symbol(n[i])) 
f <- substitute(y~f)

(I didn't try it. Most likely it doesn't quite work.)

However, what's wrong with 

lm(y ~ ., data=my.data.frame)

??

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907