[R] Specifying formula inside a function

[Mark Seeto]

Hello,

How does one specify a formula to lm inside a function (with variable
names not known in advance) and have the formula appear explicitly in
the output?

For example,

f <- function(d) {
  in.model <- sample(c(0,1), ncol(d)-1, replace=T)
  current.model <- lm(paste(names(d)[1], "~",
paste(names(d[2:ncol(d)])[which(in.model == 1)], collapse= "+")),
data=d)  #***
  return(current.model)
}
x1 <- rnorm(50,0,1)
x2 <- rnorm(50,0,1)
x3 <- rnorm(50,0,1)
x4 <- rnorm(50,0,1)
y <- rnorm(50,0,1)
d <- data.frame(y, x1, x2, x3, x4)
f(d)

Call:
lm(formula = paste(names(d)[1], "~",
paste(names(d[2:ncol(d)])[which(in.model ==     1)], collapse = "+")),
data = d)

Coefficients:
(Intercept)           x3           x4
    -0.1087       0.2830       0.1024

How can I specify the formula in the line marked *** so that the
output will show "formula = y ~ x3 + x4" instead of "formula =
paste..."?

Thanks for any help you can give.

Regards,
Mark
-- 
Mark Seeto
Statistician

National Acoustic Laboratories
A Division of Australian Hearing