Concatenate I x J*2 x K matrix in I*J x 2 x K matrix

Hi Guys,

I was using this code line for concatenate a [8 x 4 x 6] matrix in a [16 x 2 x 6] matrix:

X = [x(:,1:2,:); x(:,3:4,:)];

Now, I am trying to convert a [200 x 200 x 11] matrix in a [40000 x 2 x 11] matrix, using the code line before mentioned:

X = [x(:,1:2,:); x(:,3:4,:); x(:,5:6,:); x(:,7:8,:); x(:,9:10,:); x(:,11:12,:); x(:,13:14,:); x(:,15:16,:); x(:,17:18,:); x(:,19:20,:); ...

(and so on)

x(:,181:182,:); x(:,183:184,:); x(:,185:186,:); x(:,187:188,:); x(:,189:190,:); x(:,191:192,:); x(:,193:194,:); x(:,195:196,:); x(:,197:198,:); x(:,199:200,:)];

It works, but I can do the same with a for loop (or another approach), and for general matrix array?

[I x J*2 x K] to [I*J x 2 x K]

Thanks for your help in advance.

Answer 1

[Stephen23]

Use reshape and permute, e.g. for two columns:

>> A = randi(9,8,4,6); % fake data
>> A(:,:,1)
ans =
   9   1   4   6
   7   9   7   7
   5   6   3   4
   6   5   3   5
   2   5   3   6
   7   2   5   9
   1   5   5   2
   5   6   4   1
>> B0 = [A(:,1:2,:);A(:,3:4,:)]; % your method for comparison
>> [R,~,P] = size(A);
>> B1 = reshape(permute(reshape(A,R,2,[],P),[1,3,2,4]),[],2,P);

And checking:

>> isequal(B0,B1)
ans = 1
>> B0(:,:,1)
ans =
   9   1
   7   9
   5   6
   6   5
   2   5
   7   2
   1   5
   5   6
   4   6
   7   7
   3   4
   3   5
   3   6
   5   9
   5   2
   4   1
>> B1(:,:,1)
ans =
   9   1
   7   9
   5   6
   6   5
   2   5
   7   2
   1   5
   5   6
   4   6
   7   7
   3   4
   3   5
   3   6
   5   9
   5   2
   4   1

An example with six columns:

>> A = randi(9,3,6,5); % fake data
>> A(:,:,1)
ans =
   2   3   8   8   2   6
   5   5   1   5   6   7
   2   2   1   8   1   1
>> B0 = [A(:,1:2,:);A(:,3:4,:);A(:,5:6,:)]; % your method for comparison
>> [R,~,P] = size(A);
>> B1 = reshape(permute(reshape(A,R,2,[],P),[1,3,2,4]),[],2,P);

And checking:

>> isequal(B0,B1)
ans = 1
>> B0(:,:,1)
ans =
   2   3
   5   5
   2   2
   8   8
   1   5
   1   8
   2   6
   6   7
   1   1
>> B1(:,:,1)
ans =
   2   3
   5   5
   2   2
   8   8
   1   5
   1   8
   2   6
   6   7
   1   1

[Juan Pablo]

Thanks for you help!. The cole provide me the matrix required.