The Art of R Programming

More on the Vector/Matrix Distinction

At the beginning of the chapter, I said that a matrix is just a vector but with two additional attributes: the number of rows and the number of columns. Here, we’ll take a closer look at the vector nature of matrices. Consider this example:

> z <- matrix(1:8,nrow=4)
> z
     [,1] [,2]
[1,]    1    5
[2,]    2    6
[3,]    3    7
[4,]    4    8

As z is still a vector, we can query its length:

> length(z)
[1] 8

But as a matrix, z is a bit more than a vector:

> class(z)
[1] "matrix"
> attributes(z)
$dim
[1] 4 2

In other words, there actually is a matrix class, in the object-oriented programming sense. As noted in Chapter 1, most of R consists of S3 classes, whose components are denoted by dollar signs. The matrix class has one attribute, named ...