Continuing your example below, x[4] <- list(NULL)
I won't try to defend the semantics,which have been complained about before. However, note that with lists, x[i] is the list which consists of one member, the ith component of x, which is not the same as x[[i]], the ith component, itself; so the assignment above sets the list that contains the 4th component of x to the list that contains NULL, doing what you desire. For similar reasons, x <- c(x,list(NULL)) would also work. I believe all of this is documented in the man page for "[" ; but I grant that it takes some close reading and experimentation to get it. -- Bert Gunter Genentech Nonclinical Statistics -----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of Kynn Jones Sent: Friday, May 22, 2009 3:52 PM To: r-help@r-project.org Subject: [R] how to insert NULLs in lists? I'm an experienced programmer, but learning R is making me lose the little hair I have left... > list(NULL) [[1]] NULL > length(list(NULL)) [1] 1 > x <- list() > x[[1]] <- NULL > x list() > length(x) [1] 0 >From the above experiment, it is clear that, although one can create a one-element list consisting of a NULL element, one can't get the same result by assigning NULL to the first element of an empty list. And it gets worse: > x <- list(1, 2, 3) > length(x) [1] 3 > x[[2]] <- NULL > length(x) [1] 2 I just could NOT believe my eyes! Am I going crazy??? What I'm trying to do is so simple and straightforward: I want to be able to append NULL to a list, and, after the appending, have the last element of the list be NULL. Is that so unreasonable? How can it be done? TIA! Kynn [[alternative HTML version deleted]] ______________________________________________ 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. ______________________________________________ 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.