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Using repelem without prior knowledge of the number of matrix dimensions

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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?

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Accepted Answer

Stephen Cobeldick
Stephen Cobeldick on 6 Feb 2017
Edited: Stephen Cobeldick on 6 Feb 2017
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.

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Emmanouil
Emmanouil on 6 Feb 2017
Works like a charm! I did not know I could do this with a cell array. Thanx!

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More Answers (1)

KSSV
KSSV on 6 Feb 2017
Edited: KSSV on 6 Feb 2017
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.

  3 Comments

Emmanouil
Emmanouil on 6 Feb 2017
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
KSSV on 6 Feb 2017
Let it be..you can generate [1 1 x] using [ones(length(size(A))-1) x]
Emmanouil
Emmanouil on 6 Feb 2017
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.

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