Barry Rowlingson wrote: > 2008/11/3 <[EMAIL PROTECTED]>: > > >> So how do I detect the NULL at r[1]? >> > > How can you detect what is not there? > > Single square brackets on a list give you a list. Double square > brackets give you the elements. > > is.null(r[[1]]) should be TRUE. >
interestingly: (l = list(1, NULL)) [[1]] [1] 1 [[2]] NULL l = list(1); l[[2]] = NULL; l [[1]] [1] 1 l = as.list(1:3); l[[2]] = NULL; l [[1]] [1] 1 [[2]] [1] 2 you can have NULL as an element on a list, but assigning NULL to an element of a list removes the element rather than makes it a NULL. i find it more coherent if l[i] would remove the element (as it does) while l[[i]] would assign NULL to it (as it doesn't), OR if list(1, NULL) would return a list of 1 element. note, x = NULL *assigns* NULL to x rather than removes x: x Error: object "x" not found x = NULL; x NULL vQ ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
