How to find the maximum value of the first column in multiple matrices excluding the row we selected?

Suppose i have created a matrix say X=rand([6,3,2]);

How to find the maximum element in the first column of both the matrices excluding the row we selected ???

e.g: Here i am considering 1:6 (row) as nodes.Suppose i have selected node 2, then we ve to find max element from node 1,3,4,5,6 in the first column. Similarly, from the second matrix also we need to find the maximum element from the first column excluding the row we selected.

Answer 1

[Hari]

Hi chan,

I understand that you have a 3D matrix X with dimensions [6, 3, 2], and you want to find the maximum value in the first column of each 2D matrix while excluding a specified row.

I assume you want to perform this operation for both matrices along the third dimension of X and that the selected row is consistent across both matrices.

• Select the Row to Exclude: Determine the index of the row you want to exclude. For example, if you want to exclude the second row, set "selectedRow = 2"
• Extract the First Column: For each matrix in the third dimension, extract the first column and exclude the selected row.

selectedRow = 2; % Example: exclude the second row
matrix1 = X(:,:,1);
matrix2 = X(:,:,2);

• Remove the Selected Row: Remove the specified row from the first column of each matrix.

firstColMatrix1 = matrix1(:,1);
firstColMatrix1(selectedRow) = []; % Exclude the selected row

firstColMatrix2 = matrix2(:,1);
firstColMatrix2(selectedRow) = []; % Exclude the selected row

• Find the Maximum Value: Compute the maximum value of the remaining elements in the first column for each matrix.

maxValMatrix1 = max(firstColMatrix1);
maxValMatrix2 = max(firstColMatrix2);

• Display the Results: Output the maximum values for each matrix.

disp(['Maximum in first column of matrix 1 (excluding row ', num2str(selectedRow), '): ', num2str(maxValMatrix1)]);
disp(['Maximum in first column of matrix 2 (excluding row ', num2str(selectedRow), '): ', num2str(maxValMatrix2)]);

Output for a sample matrix generated (using "random" function):

X(:,:,1) =

0.9791 0.4139 0.7391

0.5493 0.4923 0.9542

0.3304 0.6947 0.0319

0.6195 0.9727 0.3569

0.3606 0.3278 0.6627

0.7565 0.8378 0.2815

X(:,:,2) =

0.2304 0.3488 0.7311

0.7111 0.4513 0.1378

0.6246 0.2409 0.8367

0.5906 0.7150 0.1386

0.6604 0.8562 0.5882

0.0476 0.2815 0.3662

Maximum in first column of matrix 1 (excluding row 2): 0.97913

Maximum in first column of matrix 2 (excluding row 2): 0.66044

References:

• Refer to the documentation of "max" for finding maximum values: https://www.mathworks.com/help/matlab/ref/max.html
• Refer to the documentation of "rand" for generating random matrices: https://www.mathworks.com/help/matlab/ref/rand.html

Hope this helps!

Answer 2

[Walter Roberson]

X = rand([6,3,2]);
Selected_Row = 2;
max_by_column = max(X(setdiff(1:end, Selected_Row), :, :), [], 1)

max_by_column = 
max_by_column(:,:,1) =

    0.9760    0.8972    0.9155


max_by_column(:,:,2) =

    0.7232    0.9829    0.8969