Rotate a Matrix in R

Question

I have a matrix in R like this:

|1|2|3|
|1|2|3|
|1|2|3|

Is there an easy way to rotate the entire matrix by 90 degrees clockwise to get the

Answer 1

R methods to rotate a matrix 90 degrees and -90 degrees

#first reverse, then transpose, it's the same as rotate 90 degrees
rotate_clockwise         <- function(x) { t(     apply(x, 2, rev))}
#first transpose, then reverse, it's the same as rotate -90 degrees:
rotate_counter_clockwise <- function(x) { apply(     t(x),2, rev)}

#or if you want a library to help make things easier to read:
#install.packages("pracma")
library(pracma)
rotate_one_eighty <- function(x) { rot90(x, 2) }
rotate_two_seventy <- function(x) { rot90(x, -1) }

foo = matrix(1:9, 3)
foo

foo = rotate_clockwise(foo)
foo

foo = rotate_counter_clockwise(foo)
foo

foo = rotate_one_eighty(foo)
foo

Prints:

     [,1] [,2] [,3]
[1,]    1    4    7          #original matrix
[2,]    2    5    8
[3,]    3    6    9
     [,1] [,2] [,3]
[1,]    3    2    1
[2,]    6    5    4          #rotated 90 degrees
[3,]    9    8    7
     [,1] [,2] [,3]
[1,]    1    4    7
[2,]    2    5    8          #rotated -90 degrees
[3,]    3    6    9
     [,1] [,2] [,3]
[1,]    9    6    3
[2,]    8    5    2          #rotated 180 degrees
[3,]    7    4    1

Notice that rotating a matrix clockwise, then counterclockwise returns the numbers to their original position, then rotating by 180 is like rotating by 90 twice.