MATLAB: Vector Manipulation into a matrix

matrixmatrix manipulationvector

I have a vector, A, of dimensions 21-by-1. How would I be able to manipulate this matrix such that:

A = [a;b;c;d;e;f;g;h;i;…]

Becomes a 3-by-7 matrix, B:

B = [c,b,a;f,e,d;i,h,g,…]

Any help would be much appreciated! Thanks.

Best Answer

Hi Daniel,

This can be solved by first using the reshape function and then performing the circular shift operation.

% Suppose the vector is a - of length 21
a = rand(21,1); % random column vector 21-by-1
% Now use the reshape operation to the desired size
aReshape = reshape(a,3,7); % Size is 3-by-7
% Store the first row in a variable
temp = aReshape(1,:);
% Replace the first row with the third row
aReshape(1,:) = aReshape(3,:);
% Replace the third row with the first row
aReshape(3,:) = temp;
out = aReshape;

The documentation link for the reshape function is

https://www.mathworks.com/help/matlab/ref/reshape.html

Hope this helps.

Regards,

Sriram

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Hi Abdulhakim,

The mean and reshape functions are helpful for your case. Here is the code that does what is asked for.

% Consider the input matrix is a
a = rand(30,70);
% Reshape the matrix such a way you have only 3 rows
aReshape = reshape(a,3,[]); % This turns up to 3 x 700
% Use the mean function
avg = mean(aReshape); % This returns the average of 3 elements in each column (1 x 700)
% Now to get the desired ouput in matrix form, perform the reshape again
out = reshape(avg,[],70); % Output size is (10 x 70)

The links to the document page of mean and reshape functions are:

https://www.mathworks.com/help/matlab/ref/mean.html