# concatenate different matrices with different dimensions

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Edited: Shantanu Dixit on 1 Jul 2023
Hello, I am obtaining 3 matrices with two colums each of then (the first column contains the time and the second column contains the acceleration) that represents the acceleration components of earthquake signals that can be represented as X, Y and Z matrices. So, these matrices may have the following size: X (520x2), Y(480x2) and Z(500x2) as an example. If I want to concatenate the matrices horizontally using this command:
data = horzcat(X,Y,Z), it will not work as they have different sizes.
The final size of the matrix (data) should be 520x6 (based on the highest length of colums of the three matrices X,Y and Z). So, zeros should be added at the end of each matrix with lower column size convert Y(480x2) and and Z(500x2) into Y(520x2) and Z(520x2) and then the three matrices be concatenated horizontally to create the matrix data(520x6). Thank you for your help.
Thank you very much. It works perfectly :).

Shantanu Dixit on 29 Jun 2023
Edited: Shantanu Dixit on 1 Jul 2023
Hi Jorge,
Yes you are right, horzcat requires the number of rows to be the same and for that padding needs to be done as you've explained in your question.
• Max number of rows among the three matrices are 520 or can be found through as well
maxRows = max([size(X, 1), size(Y, 1), size(Z, 1)]);
• Pad the matrices Y and Z with zeros at the end to match the maximum number of rows using the padarray() function, Since zeros need to be added at the end you need to use 'post' as the argument.
Y = padarray(Y, [maxRows - size(Y, 1), 0], 'post');
Z = padarray(Z, [maxRows - size(Z, 1), 0], 'post');
• Number of rows are same now, use horzcat to concatenate the matrices horizontally.
Refer to the documentation:
Thank you very much :). It is very usefull.

Sushma Swaraj on 29 Jun 2023
Hi,
Assuming you have X,Y and Z matrices with different sizes:
% Determine the maximum no.of rows among X,Y and Z
maxRows = max([size(X, 1), size(Y, 1), size(Z, 1)]);
% Create zero matrices to match the no.of rows
Y_zeros = zeros(maxRows, size(Y, 2));
Z_zeros = zeros(maxRows, size(Z, 2));
% Assign the original data to the zero matrices
Y_zeros(1:size(Y, 1), :) = Y;
Z_zeros(1:size(Z, 1), :) = Z;
% Concatenate X,Y_zeros and Z_zeros horizontally
data = horzcat(X, Y_zeros, Z_zeros);
Hope it helps!
Thank you very much. It works perfectly.

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