[R] Switch two rows in a matrix

[Ling, Gary (Electronic Trading)]

A <- matrix(rnorm(16)4,4)
o <- c(1,3,2,4)
A[o,o]


-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
On Behalf Of Zhang Yanwei - Princeton-MRAm
Sent: Thursday, August 07, 2008 10:31 AM
To: r-help at r-project.org
Subject: [R] Switch two rows in a matrix


Hi all,
  I have a 4 by 4 matrix, and I want to switch row 2 and row 3 first,
then switch column 2 and column 3. Is there an easy way to do it?
The following is a tedious way to get what I want. But I wonder if there
is a way to simplify this.

 > a=matrix(rnorm(16),4,4)
> a
            [,1]       [,2]        [,3]       [,4]
[1,]  0.33833811 -0.9422273 -0.06181611 -1.8346134
[2,] -0.68167996  0.2004836  0.71079887 -1.1590184
[3,]  0.07811688  0.1338694 -1.61262688  0.2988365
[4,]  0.21869786 -1.6356661 -0.13694344 -1.2121355
> b=a
> b[2,]=a[3,]
> b[3,]=a[2,]
> b
            [,1]       [,2]        [,3]       [,4]
[1,]  0.33833811 -0.9422273 -0.06181611 -1.8346134
[2,]  0.07811688  0.1338694 -1.61262688  0.2988365
[3,] -0.68167996  0.2004836  0.71079887 -1.1590184
[4,]  0.21869786 -1.6356661 -0.13694344 -1.2121355
> c=b
> c[,2]=b[,3]
> c[,3]=b[,2]
> c
            [,1]        [,2]       [,3]       [,4]
[1,]  0.33833811 -0.06181611 -0.9422273 -1.8346134
[2,]  0.07811688 -1.61262688  0.1338694  0.2988365
[3,] -0.68167996  0.71079887  0.2004836 -1.1590184
[4,]  0.21869786 -0.13694344 -1.6356661 -1.2121355


Sincerely,
Yanwei Zhang
Department of Actuarial Research and Modeling
Munich Re America
Tel: 609-275-2176
Email: yzhang at munichreamerica.com<mailto:yzhang at munichreamerica.com>


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