Beware x[TRUE] returns the same as x[] only if x is NOT a zero-length vector (at least until R 2.5.1):
> numeric(0)[] numeric(0) > numeric(0)[TRUE] [1] NA Enrique > -----Original Message----- > ------------------------------ > > Message: 7 > Date: Mon, 10 Mar 2008 02:29:32 +0800 > From: "Laurent Gautier" <[EMAIL PROTECTED]> > Subject: Re: [Rd] extract function "[" and empty index > To: "Gabor Grothendieck" <[EMAIL PROTECTED]> > Cc: r-devel@r-project.org > Message-ID: > <[EMAIL PROTECTED]> > Content-Type: text/plain; charset=ISO-8859-1 > > Thanks, I was forgetting the recycling rule. > > > L. > > > 2008/3/9, Gabor Grothendieck <[EMAIL PROTECTED]>: > > Use TRUE. > > > > > > On Sun, Mar 9, 2008 at 5:05 AM, Laurent Gautier > <[EMAIL PROTECTED]> wrote: > > > Dear list, > > > > > > I am having a question regarding the extract function "[". > > > > > > The man page says that one usage with k-dimensional arrays is to > > > specify k indices to "[", with an empty index indicating that all > > > entries in that dimension are selected. > > > > > > The question is the following: is there an R object > qualifying as an > > > "empty index" ? I understand that the lazy evaluation of > parameters > > > allows one to > > > have genuinely missing parameters, but I would like to > have an object > > > instead. I understand that one can always have an > if/else workaround, > > > but I thought should ask, just in case. > > > > > > I tried with NULL but with little success, as it appears > to give the > > > same results > > > as an empty vector. > > > > m = matrix(1, 2, 2) > > > > m[1, NULL] > > > numeric(0) > > > > m[1, integer(0)] > > > numeric(0) > > > > > > Since I was at it, I noted that the result obtained with > "numeric(0)" > > > definitely makes sense but could as well be seen as > challenging the > > > concept of an empty index presented in the man page (One > could somehow > > > expect the presence of an object meaning "everything" > rather than > > > "missingness" meaning it). > > > > > > > > > Thanks, > > > > > > > > > Laurent > > > > > > > > ______________________________________________ > > > R-devel@r-project.org mailing list > > > https://stat.ethz.ch/mailman/listinfo/r-devel > > > > > > > > -- ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
