Dim Attribute of an Object
DESCRIPTION:
Returns or changes the dim attribute, which describes the dimensions of a matrix, data frame or array.
USAGE: 
dim(x)
dim(x) <- value
REQUIRED ARGUMENTS:
x:
any object.
OPTIONAL ARGUMENTS:
value:
numeric vector suitable to be the dimensions of x(missing values are not allowed), or NULL.
VALUE:
integer vector of the dimensions of x, if any; and NULL if x does not have dimensions.
SIDE EFFECTS:
assigning to dim(x) establishes or changes the dim attribute of x if it is an array or matrix; no re-ordering of the elements of x is implied.
DETAILS:
This is a generic function, dim has a method for data frames, which counts the length of the row.names attribute and the number of columns. You may not change the dimensions of a data frame.

Arrays and matrices have a dim attribute which is an integer vector, with the property that prod(dim(x))==length (x). This attribute identifies an object as an array.

SEE ALSO:
dimnames , ncol , array , matrix , data.frame , length .
EXAMPLES: 
dim(iris) # returns c(50, 4, 3)


length(dim(y)) # number of dimensions of y


if(!is.null(dim(z))) { .. z .. } # do not operate on non-array data
if(is.array(z)) { .. z .. } # better way to do the same thing