How do you convert a 4D matrix into a N by M

I've got a 4D array from a nested for loop [Month, day, record [pair of values] ] that I need to convert into a single N by M matrix in order to run a probablilty matrix analysis....any ideas on the conversion from 4D to 2D?

Answer 1

[Wayne King]

Hi Oliver, you can use reshape() but you have to be mindful of how the elements are filled in the 2-D matrix.

For example:

x = randn(2,2,2);
x1 = reshape(x,4,2);

[Jan]

The PERMUTE command might be helpful in addition.

Answer 2

[Andrei Bobrov]

e.g.

a4d = randi(125,[2 2 2 2])

[s1,ign1,s3,ign2] = size(a4d)
a2d = reshape(permute(a4d,[1 3 2 4]),s1*s3,[])

Answer 3

[Image Analyst]

One way to do it is to create your 2D array at the same time as you created your 4D array - inside your 4 nested for loops that you already have. Use a counter, like "row"

row = 1;
array2D = zeros(10*11*12*13, 1); % Preallocate
for d1 = 1:10
  for d2 = 1:11
    for d3 = 1:12
      for d4 = 1:13
        % Create your 4D array
        array4D(d1,d2,d3,d4) = theValue;
        % Now create your 2D array
        array2D(row, 1) = d1;
        array2D(row, 2) = d2;
        array2D(row, 3) = d3;
        array2D(row, 4) = d4;
        array2D(row, 5) = theValue;
        % Now increment the row number
        row = row + 1;
      end
    end
  end
end

Answer 4

[Oliver]

Maybe my approach is wrong....is there a way of creating a nested for loop and getting an output strainght to a vector?

[Fangjun Jiang]

Certainly. Just write nested for-loops. It depends on the order you want, right. The easiest way doesn't require any loop. For example, a=rand(2,3,4,5); b=a(:).