Using repelem without prior knowledge of the number of matrix dimensions

Hello,

I have a matrix A that can be either 3D, 4D, 5D etc. I want to repeat the elements of the last dimension x times. This can be accomplished by using the following expressions: repelem(A,1,1,x) for 3D and repelem(A,1,1,1,x) for 4D matrices. However, since I do not know the number of matrix dimensions in advance, these expressions do not help me. Ideally, I would like to use repelem like repmat e.g. repelem(A,[1,1,x]) for 3D and repelem(A,[1,1,1,x]) for 4D matrices. However these expressions are not valid. I know I can do this combining reshape and repmat but I would like to know if there is a more compact way since there is a repelem function (I would also like to avoid using eval). Any ideas?

Answer 1

[Stephen23]

It is easy to generate a comma separated list from a cell array, and use this to specify the repelem inputs:

 x = 10;
 C = num2cell([ones(1,ndims(A)-1),x]);
 out = repelem(A, C{:})

Note that you will need to consider scalar and column vector A as special cases.

[Emmanouil]

Works like a charm! I did not know I could do this with a cell array. Thanx!

Answer 2

[KSSV]

Use a if condition on length(size(A)). If A is 3D your length(size(A)) will be 3 and you have to use repelem(A,1,1,x). Like wise if A is 4D, length(size(A)) will be 4.

[Emmanouil]

Thanx, this is indeed a valid approach but not so neat. Matrix A can be 3D, 4D, 5D etc, there is no limit in the number of matrix dimensions.

[KSSV]

Let it be..you can generate [1 1 x] using [ones(length(size(A))-1) x]

[Emmanouil]

I know I can do this, this was my initial intention as I write in the question. The problem is that the expression repelem(A,[1,1,x]) is not valid.