:) Well, yes, but what do you do with a named vector if you want to remove an element by name?
It is not general: you cannot do that on vectors, matrices, arrays and all inherited objects anyway. Using a negative index is a standard and throughout practice of deleting elements in R. Surely one can have exceptions or extended behaviour for different classes, like list and data.frame here, but I cannot say it is really necessary to have it in order to produce a clean, easily readable and reliable code. Yes, I know now, this NULL assignment has existed there for long time and I am not about to propose its removal, but I really do not see a good reason for having it either. I would never use it in my code either. After all you do not assign NULLs to elements of a non-list vector or matrix or array. Best, Oleg Gabor Grothendieck wrote: > But what about by name? > > a <- list(a = 1, b = 2, c = 3) > > a$b <- NULL > > > On Feb 13, 2008 9:39 AM, Oleg Sklyar <[EMAIL PROTECTED]> wrote: >> Hmm, I think the pretty traditional R style does the job... >> >> a = list(1,2,3) >> a[-2] >> >> So I really do not see a good reason for doing a[2] = NULL instead of a >> = a[-2] >> >> >> Jeffrey J. Hallman wrote: >>> >From your tone, I gather you don't much like this behavior, and I can see >>> >your >>> point, as it not very intuitive that setting a list element to NULL deletes >>> any existing element at that index. But is there a better way to delete an >>> element from a list? Maybe there should be. >>> >>> Jeff >>> >>> Prof Brian Ripley <[EMAIL PROTECTED]> writes: >>>>> I have just came across an (unexpected to me) behaviour of lists when >>>>> assigning NULLs to list elements. I understand that a NULL is a valid R >>>>> object, thus assigning a NULL to a list element should yield exactly the >>>>> same result as assigning any other object. So I was surprised when >>>>> assigning a NULL in fact removed the element from the list. Is this an >>>>> intended behaviour? If so, does anybody know where is it documented and >>>>> what is a good way around? >>>> Yes, it was apparently intended: R has long done this. >>>> >>>> x <- list(a=c(1L,2L), b=matrix(runif(4),2,2), c=LETTERS[1:3]) >>>> x[2] <- list(NULL) >>>> >>>> is what I think you are intending. >>>> >>>> See e.g. the comment in subassign.c >>>> >>>> /* If "val" is NULL, this is an element deletion */ >>>> /* if there is a match to "nlist" otherwise "x" */ >>>> /* is unchanged. The attributes need adjustment. */ >> -- >> Dr Oleg Sklyar * EBI-EMBL, Cambridge CB10 1SD, UK * +44-1223-494466 >> >> ______________________________________________ >> >> R-devel@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-devel >> -- Dr Oleg Sklyar * EBI-EMBL, Cambridge CB10 1SD, UK * +44-1223-494466 ______________________________________________ R-devel@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-devel
