# [R] list of matrices --> array

Murat Tasan mmuurr at gmail.com
Sun Feb 17 19:42:29 CET 2013

```thanks to all!
they're exactly what i wanted.

cheers,

-m

On Sun, Feb 17, 2013 at 9:41 AM, Tony Plate <taplate at gmail.com> wrote:
> abind() (from package 'abind') can take a list of arrays as its first
> argument, so in general, no need for do.call() with abind().
>
> As another poster pointed out, simplify2array() can also be used; while
> abind() gives more options regarding which dimension is created and how
> dimension names are constructed.
>
>> x <- list(A=cbind(X=c(a=1,b=2,c=3,d=4),Y=5:8,Z=9:12),
>> B=cbind(X=c(a=13,b=14,c=15,d=16),Y=17:20,Z=21:24))
> \$A
>   X Y  Z
> a 1 5  9
> b 2 6 10
> c 3 7 11
> d 4 8 12
>
> \$B
>    X  Y  Z
> a 13 17 21
> b 14 18 22
> c 15 19 23
> d 16 20 24
>
>>
>> dim(abind(x, along=3))
>  4 3 2
>> dim(abind(x, along=1.5))
>  4 2 3
>> dim(abind(x, along=0.5))
>  2 4 3
>> dim(abind(x, along=1, hier.names=T)) # construct rownames in a
>> hierarchical manner A.a, A.b, etc
>  8 3
>> dim(abind(x, along=2, hier.names=T)) # construct colnames in a
>> hierarchical manner
>  4 6
>> abind(x, along=2, hier.names=T)
>   A.X A.Y A.Z B.X B.Y B.Z
> a   1   5   9  13  17  21
> b   2   6  10  14  18  22
> c   3   7  11  15  19  23
> d   4   8  12  16  20  24
>
>>
>
> On 2/14/2013 3:53 AM, Rolf Turner wrote:
>>
>>
>> require(abind)
>> do.call(abind,c(my_list,list(along=0))) # Gives 2 x 4 x 5
>> do.call(abind,c(my_list,list(along=3))) # Gives 4 x 5 x 2
>>
>> The latter seems more natural to me.
>>
>>     cheers,
>>
>>         Rolf Turner
>>
>> On 02/14/2013 07:03 PM, Murat Tasan wrote:
>>>
>>> i'm somehow embarrassed to even ask this, but is there any built-in
>>> method for doing this:
>>>
>>> my_list <- list()
>>> my_list[] <- matrix(1:20, ncol = 5)
>>> my_list[] <- matrix(20:1, ncol = 5)
>>>
>>> now, knowing that these matrices are identical in dimension, i'd like
>>> to unfold the list to a 2x4x5 (or some other permutation of the dim
>>> sizes) array.
>>> i know i can initialize the array, then loop through my_list to fill
>>> the array, but somehow this seems inelegant.
>>> i also know i can vectorize the matrices and unlist the list, then
>>> build the array from that single vector, but this also seems inelegant
>>> (and an easy place to introduce errors/bugs).
>>>
>>> i can't seem to find any built-in that handles this already... but
>>> maybe i just haven't looked hard enough :-/
>>
>>
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