[R] dim vs length for vectors

[Gabor Grothendieck]

More generally, anything that has a dim attribute is an array 
including 1d, 2d, 3d structures with dim attributes.
Matrices have a dim attribute so matrices are arrays and
is.array(m) will be TRUE if m is a matrix.  

miguel manese <jjonphl <at> gmail.com> writes:

: 
: 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
: <ggrothendieck <at> myway.com> 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 <at> 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 <at> 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
: 
: