[R] dots expansion

[Liaw, Andy]

In addition to Gabor's comments:

There's a reason why I didn't coerce the grouping variable to a factor.
rbind()ing data frames is much more expensive than rbind()ing
arrays/matrices.  Unless your data really have different data types in
different columns, it would mostly likely be better to work with the matrix
version of them.  If you really want a data frame with the grouping variable
as a factor, you can do the coercion afterward.

Andy

> From: Gabor Grothendieck
> 
> Viet Nguyen <vietnguyen <at> fastmail.fm> writes:
> 
> > 
> > Thanks to all who helped.
> > 
> > I used your ideas and code samples to write the following (for the 
> > benefit of people who will search this list later):
> > 
> > rbind.case <- function(..., name="case", values) {
> >     dots <- list(...);
> >     if (missing(values)) values <- 1:length(dots);
> >     if (length(values)!=length(dots))
> >       stop("length(values)!=length(list(...))");
> > 
> >     eval(parse(text=
> >                paste("cbind(rbind(...), ",name,
> >                      "=rep(values, sapply(dots, nrow)))",sep="")));
> > }
> > 
> > The function is to be used with data frames. It's not as 
> good as it can 
> > be but it works for my purpose.
> 
> Regarding improvements, eliminate the semicolons at the end 
> of statements,
> place the default value for values= in the arg list to make 
> it more readable,
> use stopifnot to check args (also for readability), add a check for 
> data frames (which is mentioned after the code but not checked for, 
> and eliminate the eval and rep calculations by simply 
> lapplying over an 
> index and appending the name column to each data frame in turn:
> 
> 
> rbind.case <- function(..., name="case", values = seq(along = 
> list(...))) 
> # rbind the ... data frames together adding a column named name whose 
> # value for rows from ith argument is values[i]
> {
>    dots <- list(...)
>    stopifnot(length(dots) == length(values),
> 	   all(sapply(dots, inherits, "data.frame")))
> 
>    f <- function(i) { x <- dots[[i]]; x[,name] <- values[i]; x }
>    do.call("rbind", lapply(seq(along = dots), f))
> }
> 
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