[R] generating an expression for a formula automatically

[Sundar Dorai-Raj]

Maria Montez wrote:
> Hi!
> 
> I would like to be able to create formulas automatically. For example, I 
> want to be able to create a function that takes on two values: resp and 
> x, and then creates the proper formula to regress resp on x.
> 
> My code:
> 
> fit.main <- function(resp,x) {
>  form <- expression(paste(resp," ~ ",paste(x,sep="",collapse=" + "),sep=""))
>   z <- lm(eval(form))
>  z
> }
> main <- fit.main("y",c("x1","x2","x3","x4"))
> 
> and I get this error:
> Error in terms.default(formula, data = data) :
>         no terms component
> 
> Any suggestions?
> 
> Thanks, Maria
> 
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Hi, Maria,

Try

regr <- paste(x, collapse = "+")
form <- as.formula(sprintf("%s ~ %s", resp, regr))

HTH,

--sundar