[R] Splitting a matrix

[Bill.Venables at csiro.au]

Here is one possibility:

> set.seed(1)
> dat <- matrix(rnorm(4*16), 4, 16)
> dim(dat) <- c(4,4,4)
> dat
, , 1

           [,1]       [,2]       [,3]        [,4]
[1,] -0.6264538  0.3295078  0.5757814 -0.62124058
[2,]  0.1836433 -0.8204684 -0.3053884 -2.21469989
[3,] -0.8356286  0.4874291  1.5117812  1.12493092
[4,]  1.5952808  0.7383247  0.3898432 -0.04493361

, , 2

            [,1]        [,2]        [,3]       [,4]
[1,] -0.01619026  0.91897737  0.61982575 -0.4781501
[2,]  0.94383621  0.78213630 -0.05612874  0.4179416
[3,]  0.82122120  0.07456498 -0.15579551  1.3586796
[4,]  0.59390132 -1.98935170 -1.47075238 -0.1027877

, , 3

            [,1]       [,2]       [,3]       [,4]
[1,]  0.38767161 -0.3942900 -0.1645236 -0.6887557
[2,] -0.05380504 -0.0593134 -0.2533617 -0.7074952
[3,] -1.37705956  1.1000254  0.6969634  0.3645820
[4,] -0.41499456  0.7631757  0.5566632  0.7685329

, , 4

           [,1]       [,2]       [,3]        [,4]
[1,] -0.1123462  0.3411197 -0.3672215  2.40161776
[2,]  0.8811077 -1.1293631 -1.0441346 -0.03924000
[3,]  0.3981059  1.4330237  0.5697196  0.68973936
[4,] -0.6120264  1.9803999 -0.1350546  0.02800216

>  

-----Original Message-----
From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf Of Megh Dal
Sent: Thursday, 16 September 2010 5:43 PM
To: r-help at stat.math.ethz.ch
Subject: [R] Splitting a matrix

Hi, I was trying to split the following matrix "dat":

> set.seed(1)
> dat <- matrix(rnorm(4*16), 4, 16)
> dat
           [,1]       [,2]       [,3]        [,4]        [,5]        [,6]        [,7]       [,8]        [,9]      [,10]      [,11]
[1,] -0.6264538  0.3295078  0.5757814 -0.62124058 -0.01619026  0.91897737  0.61982575 -0.4781501  0.38767161 -0.3942900 -0.1645236
[2,]  0.1836433 -0.8204684 -0.3053884 -2.21469989  0.94383621  0.78213630 -0.05612874  0.4179416 -0.05380504 -0.0593134 -0.2533617
[3,] -0.8356286  0.4874291  1.5117812  1.12493092  0.82122120  0.07456498 -0.15579551  1.3586796 -1.37705956  1.1000254  0.6969634
[4,]  1.5952808  0.7383247  0.3898432 -0.04493361  0.59390132 -1.98935170 -1.47075238 -0.1027877 -0.41499456  0.7631757  0.5566632
          [,12]      [,13]      [,14]      [,15]       [,16]
[1,] -0.6887557 -0.1123462  0.3411197 -0.3672215  2.40161776
[2,] -0.7074952  0.8811077 -1.1293631 -1.0441346 -0.03924000
[3,]  0.3645820  0.3981059  1.4330237  0.5697196  0.68973936
[4,]  0.7685329 -0.6120264  1.9803999 -0.1350546  0.02800216

I want to split above one into 4 matrices (probably can be confined into a list) wherein 1st matrix consists of columns 1-4, 2nd matrix consists column 5-8 etc. Here I tried following:

> lapply(split(t(dat), c(4,8,12,16), drop=F), function(x) return(t(matrix(x, 4, 4))))
$`4`
           [,1]        [,2]        [,3]       [,4]
[1,] -0.6264538 -0.01619026  0.38767161 -0.1123462
[2,]  0.1836433  0.94383621 -0.05380504  0.8811077
[3,] -0.8356286  0.82122120 -1.37705956  0.3981059
[4,]  1.5952808  0.59390132 -0.41499456 -0.6120264

$`8`
           [,1]        [,2]       [,3]       [,4]
[1,]  0.3295078  0.91897737 -0.3942900  0.3411197
[2,] -0.8204684  0.78213630 -0.0593134 -1.1293631
[3,]  0.4874291  0.07456498  1.1000254  1.4330237
[4,]  0.7383247 -1.98935170  0.7631757  1.9803999

$`12`
           [,1]        [,2]       [,3]       [,4]
[1,]  0.5757814  0.61982575 -0.1645236 -0.3672215
[2,] -0.3053884 -0.05612874 -0.2533617 -1.0441346
[3,]  1.5117812 -0.15579551  0.6969634  0.5697196
[4,]  0.3898432 -1.47075238  0.5566632 -0.1350546

$`16`
            [,1]       [,2]       [,3]        [,4]
[1,] -0.62124058 -0.4781501 -0.6887557  2.40161776
[2,] -2.21469989  0.4179416 -0.7074952 -0.03924000
[3,]  1.12493092  1.3586796  0.3645820  0.68973936
[4,] -0.04493361 -0.1027877  0.7685329  0.02800216

However this is not that which I wanted to get. Any idea on the proper code to doing that?

Thanks

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