You are again misinterpreting because you have not read the docs, although this time I will grant that they are to some extent misleading.
First of all, a matrix _IS_ a vector: > a <- matrix(1:4, 2,2) > a[3] ## vector indexing works because it is a vector [1] 3 In fact, a matrix (or array) is a vector with a "dim" attribute. This is documented in ?matrix: "is.matrix returns TRUE if x is a vector and has a "dim" attribute of length 2) and FALSE otherwise." Your confusion arises because, despite its name, is.vector() does not actually test whether something "is" a vector (after all these are all abstractions; what it "is" is contents of memory, implemented as a linked list or some such). ?is.vector tells you: "is.vector returns TRUE if x is a vector of the specified mode having no attributes other than names. It returns FALSE otherwise." An array has a "dim" attribute, so is.vector() returns FALSE on it. But it actually _is_ ("behaves like") a vector (in column major order,actually). Now you may complain that this is confusing and I would agree. Why is it this way? I dunno -- probably due to historical quirks -- evolution is not necessarily orderly. But that's the way it is; that's the way it's documented; and tutorials will tell you about this (that's how I learned). So please stop guessing and intuiting and read the docs to understand how things work. Cheers, Bert Bert Gunter Genentech Nonclinical Biostatistics (650) 467-7374 "Data is not information. Information is not knowledge. And knowledge is certainly not wisdom." Clifford Stoll On Wed, Dec 24, 2014 at 8:45 PM, Mike Miller <mbmille...@gmail.com> wrote: > On Wed, 24 Dec 2014, Jeff Newmiller wrote: > >> On December 24, 2014 6:49:47 PM PST, Mike Miller <mbmille...@gmail.com> >> wrote: >> >>> On Wed, 24 Dec 2014, Mike Miller wrote: >>> >>>> Also, regarding the sacred text, "x A numeric." is a bit terse. The >>>> same text later refers to length(x), so I suspect that "A numeric" is >>> >>> >>>> short for "A numeric vector", but that might not mean "a vector of >>>> 'numeric' type." >>> >>> >>> >>> I just realized that numeric type includes integer so that anything of >>> type integer also is type numeric. I'm working on another message. >> >> >> >> But all numeric types in R are vectors. So although it might be a good >> idea to be redundant to aid beginners, the phrase "a numeric" is accurate. > > > > Interesting, but the data seem to contradict your theory. Here are two > examples, one with a numeric matrix, the other with a numeric array, and > both of them run in ave(). > >> x <- matrix(1:4, 2,2) > > >> is.numeric(x) > > [1] TRUE > >> is.vector(x) > > [1] FALSE > >> ave(x, gl(2,2)) > > [,1] [,2] > [1,] 1.5 3.5 > [2,] 1.5 3.5 > > >> x <- as.array(1:4) > > >> is.numeric(x) > > [1] TRUE > >> is.vector(x) > > [1] FALSE > >> ave(x, gl(2,2)) > > [1] 1.5 1.5 3.5 3.5 > > > So maybe slightly more documentation for ave() would be helpful even for > non-beginners like yourself. > > Thanks. > > Mike > > -- > Michael B. Miller, Ph.D. > University of Minnesota > http://scholar.google.com/citations?user=EV_phq4AAAAJ ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.