[R] dots expansion

[Gabor Grothendieck]

That's a good point.  Your original solution is simpler than the poster's
and likely faster than mine.  

At any rate, continuing the with simplicity, rather than performance, vein if
one does want to allow matrices or data frames then the solution I posted won't
work, even if you take away the check for data frames, since I was using the
following trick to append a column without using cbind:

	x[,"newcol"] <- whatever

That appends whatever as a column named "newcol" if x is a data frame but
gives an error if x is a matrix.  

In that case, we should use cbind, and I think the problem the poster was
having is that cbind(x, name = values) regards name as literally that and
not a variable.  To get around this we can temporarily define our own 
cbind which allows the column names to be specified.  The new cbind 
definition is elementary and neither the last line, which does the key 
processing, nor the rest of it involves any rep arithmetic, indices or evals:

rbind.case <- function(..., name = "case", values = seq(along = list(...))) 
# rbind the ... data frames or matrices together adding a column named name 
# whose value for rows from ith argument is values[i]
{

  dots <- list(...)
  stopifnot(length(dots) == length(values))

  # cbind x and y using indicated column names
  cbind <- function(x, y, names.x = colnames(x), names.y = colnames(y)) { 
    z <- base::cbind(x, y)
    colnames(z) <- c(names.x, names.y)
    z
  }

  do.call("rbind", mapply(cbind, dots, values, names.y = name, SIMPLIFY = F))

}




Liaw, Andy <andy_liaw <at> merck.com> writes:

: 
: 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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: >
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