I think the more intuitive way to think of it is that dim works only for matrices (an array being a 1 column matrix). and vectors are not matrices.
> x <- 1:5 > class(x) # numeric > dim(x) <- 5 > class(x) # array > dim(x) <- c(5,1) > class(x) # matrix > dim(x) <- c(1,5) > class(x) # matrix On Fri, 21 Jan 2005 05:35:11 +0000 (UTC), Gabor Grothendieck <[EMAIL PROTECTED]> wrote: > Olivia Lau <olau <at> fas.harvard.edu > writes: > > : > : Hi all, > : > : I'm not sure if this is a feature or a bug (and I did read the > : FAQ and the posting guide, but am still not sure). Some of my > : students have been complaining and I thought I just might ask: > : Let K be a vector of length k. If one types dim(K), you get > : NULL rather than [1] k. Is this logical? > : > : Here's the way I explain it (and maybe someone can provide a > : more accurate explanation of what's going on): R has several > : types of scalar (atomic) values, the most common of which are > : numeric, integer, logical, and character values. Arrays are > : data structures which hold only one type of atomic value. > : Arrays can be one-dimensional (vectors), two-dimensional > : (matrices), or n-dimensional. > : > : (We generally use arrays of n-1 dimensions to populate > : n-dimensional arrays -- thus, we generally use vectors to > : populate matrices, and matrices to populate 3-dimensional > : arrays, but could use any array of dimension < n-1 to populate > : an n-dimensional array.) > : > : It logically follows that when one does dim() on a vector, one > : should *not* get NULL, but should get the length of the vector > : (which one *could* obtain by doing length(), but I think this is > : less logical). I think that R should save length() for lists > : that have objects of different dimension and type. > : > > In R, vectors are not arrays: > > R> v <- 1:4 > R> dim(v) > NULL > R> is.array(v) > [1] FALSE > > R> a <- array(1:4) > R> dim(a) > [1] 4 > R> is.array(a) > [1] TRUE > > ______________________________________________ > R-help@stat.math.ethz.ch mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html > ______________________________________________ R-help@stat.math.ethz.ch mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
