在R中旋转矩阵 [英] Rotate a Matrix in R

问题描述

我在R中有一个矩阵，像这样:

I have a matrix in R like this:

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

是否有一种简单的方法将整个矩阵顺时针旋转90度以获得这些结果?

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

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

然后再次旋转90度:

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

?

推荐答案

t不会旋转条目，而是沿对角线翻转:

t does not rotate the entries, it flips along the diagonal:

x <- matrix(1:9, 3)
x
##      [,1] [,2] [,3]
## [1,]    1    4    7
## [2,]    2    5    8
## [3,]    3    6    9

t(x)
##      [,1] [,2] [,3]
## [1,]    1    2    3
## [2,]    4    5    6
## [3,]    7    8    9

R矩阵顺时针旋转90度:

您还需要在转置之前反转列:

You need to also reverse the columns prior to the transpose:

rotate <- function(x) t(apply(x, 2, rev))
rotate(x)
##      [,1] [,2] [,3]
## [1,]    3    2    1
## [2,]    6    5    4
## [3,]    9    8    7

rotate(rotate(x))
##      [,1] [,2] [,3]
## [1,]    9    6    3
## [2,]    8    5    2
## [3,]    7    4    1

rotate(rotate(rotate(x)))
##      [,1] [,2] [,3]
## [1,]    7    8    9
## [2,]    4    5    6
## [3,]    1    2    3

rotate(rotate(rotate(rotate(x))))
##      [,1] [,2] [,3]
## [1,]    1    4    7
## [2,]    2    5    8
## [3,]    3    6    9

R矩阵逆时针旋转90度:

在反转之前进行转置与逆时针旋转相同:

Doing the transpose prior to the reverse is the same as rotate counter clockwise:

foo = matrix(1:9, 3)
foo
## [,1] [,2] [,3]
## [1,]    1    4    7
## [2,]    2    5    8
## [3,]    3    6    9

foo <- apply(t(foo),2,rev)
foo

## [,1] [,2] [,3]
## [1,]    7    8    9
## [2,]    4    5    6
## [3,]    1    2    3

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