On 12/03/2009, at 3:16 AM, Szumiloski, John wrote:
Dear useRs,
I have a utility function which is meant to be a clone of ls(), except
with the option all.names=TRUE. Currently however, the function
merely
consists of a copy of the source code of ls(), except the default
value
of all.names is different. That approach has the drawback of future
inconsistency if the code for ls() ever changes. No comment on
whether
that is likely or not; I would and do object to the current
construction
in principle.
What I would like to do is rewrite the new function so that it does
very
minimal processing of its arguments, and then calls ls() with the new
arguments, somewhat in the same spirit of the Recall() function.
A challenge to me has been twofold, that this new ls() call has a
different search path, and that ls() itself has a good deal of lazy
evaluation (including possibly twice in one line, around line 11)
in it.
Getting my new function to work with all permutations of arguments,
without merely copying the code from ls(), has been futile.
I am sure I could manually enumerate the behavior for all permutations
of all the arguments to ls(), and code each case individually. I am
also sure I will not waste my time doing that. I was hoping, however,
that there was some simple trick to allow this easily, one that I have
missed. Even an explanation of why this might be a fool's errand
would
be quite helpful to my understanding of the intricacies of R
evaluation.
Does the following do what you want?
myls <- function (all.names=TRUE,pos=-1,...)
{
xxx <- pmatch(names(list(...)),"envir",nomatch=0)
if(length(xxx) && xxx>0) return(ls(all.names=all.names,pos=pos,...))
eee <- if(pos==-1) parent.frame() else as.environment(pos)
ls(all.names=all.names,envir=eee,...)
}
cheers,
Rolf Turner
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