The Art of R Programming

Adding and Deleting Matrix Rows and Columns

Technically, matrices are of fixed length and dimensions, so we cannot add or delete rows or columns. However, matrices can be reassigned, and thus we can achieve the same effect as if we had directly done additions or deletions.

Changing the Size of a Matrix

Recall how we reassign vectors to change their size:

> x
[1] 12  5 13 16  8
> x <- c(x,20)  # append 20
> x
[1] 12  5 13 16  8 20
> x <- c(x[1:3],20,x[4:6])  # insert 20
> x
[1] 12  5 13 20 16  8 20
> x <- x[-2:-4]  # delete elements 2 through 4
> x
[1] 12 16  8 20

In the first case, x is originally of length 5, which we extend to 6 via concatenation and then reassignment. We didn’t literally change the length of x but instead created a new vector from x and ...