[R] Matrix to list

[Marc Schwartz]

On Sep 3, 2010, at 7:48 AM, Ron Michael wrote:

> Dear all, suppose I have following matrix:
>  
>> mat <- matrix(rnorm(25), 5)
>> 
>> mat
>             [,1]       [,2]        [,3]       [,4]       [,5]
> [1,]  0.97056228 -1.3278509 -0.73511792  2.1650629 -0.4411997
> [2,]  0.58613700 -0.2559899 -1.18334248 -1.4990907  1.8138846
> [3,] -1.03333313  2.0227887  0.89622681  0.6483973 -1.5523283
> [4,]  0.38968833  0.2490004 -0.02301061 -0.2705150 -0.9237268
> [5,]  0.03306289 -0.4022751 -0.44404905 -1.6810542 -0.1016683
> 
> Now from "mat" I would like to create a "list" object where i-th column of "mat" will represent i-th element of that list object.
>  
> I am looking for some way to avoid for loop. It will be really helpful if somebody points me on that.
>  
> Thanks,


Try this:

set.seed(1)

mat <- matrix(rnorm(25), 5)

> mat
           [,1]       [,2]       [,3]        [,4]        [,5]
[1,] -0.6264538 -0.8204684  1.5117812 -0.04493361  0.91897737
[2,]  0.1836433  0.4874291  0.3898432 -0.01619026  0.78213630
[3,] -0.8356286  0.7383247 -0.6212406  0.94383621  0.07456498
[4,]  1.5952808  0.5757814 -2.2146999  0.82122120 -1.98935170
[5,]  0.3295078 -0.3053884  1.1249309  0.59390132  0.61982575


# Coerce 'mat' to a data frame, then to a 'normal' list

> as.list(as.data.frame(mat))
$V1
[1] -0.6264538  0.1836433 -0.8356286  1.5952808  0.3295078

$V2
[1] -0.8204684  0.4874291  0.7383247  0.5757814 -0.3053884

$V3
[1]  1.5117812  0.3898432 -0.6212406 -2.2146999  1.1249309

$V4
[1] -0.04493361 -0.01619026  0.94383621  0.82122120  0.59390132

$V5
[1]  0.91897737  0.78213630  0.07456498 -1.98935170  0.61982575



You can argue that the coercion to a list is redundant, since a data frame is a list, but it may depend upon what you then want to do with the data.

HTH,

Marc Schwartz