Store all results obtained from a for loop inside a matrix

Question

Alberto Acri 2023-7-23

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1999508-store-all-results-obtained-from-a-for-loop-inside-a-matrix

编辑： Stephen23 2023-7-23

Hi. I need to transform the matrix 'matrix' to 'matrix_out' by inserting the number '0' inside the matrix 'matrix' in reference to the coordinates of the matrix 'coord'.

I tried this for loop and it works, but I don't understand how to return all the results of the for loop to the matrix matrix_out.

matrix = [5,6,14,25; 14,55,44,16; 98,65,34,75; 67,89,21,88];
coord = [1,1; 1,3; 2,2; 3,2; 4,3; 4,4];
for K = 1:length(coord)
    A = coord(K,:);
    A_x = A(1);
    A_y = A(2);
    matrix_out = matrix;
    matrix_out(A_x,A_y) = 0;
end
% RESULT: matrix_out = [0,6,0,25; 14,0,44,16; 98,0,34,75; 67,89,0,0];

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Answer 1

Stephen23 2023-7-23

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https://ww2.mathworks.cn/matlabcentral/answers/1999508-store-all-results-obtained-from-a-for-loop-inside-a-matrix#answer_1277273

编辑：Stephen23 2023-7-23

在 MATLAB Online 中打开

The simpler MATLAB approach is to use SUB2IND:

matrix = [5,6,14,25; 14,55,44,16; 98,65,34,75; 67,89,21,88];
coord = [1,1; 1,3; 2,2; 3,2; 4,3; 4,4];
idx = sub2ind(size(matrix),coord(:,1),coord(:,2));
matrix(idx) = 0
matrix = 4×4
     0     6     0    25
    14     0    44    16
    98     0    34    75
    67    89     0     0

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Answer 2

Samya 2023-7-23

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Hi, from my understanding there is a very minor change in your code,

To achieve the desired result, you need to initialize the `matrix_out` variable before the loop and update it within the loop. Here's the modified code:

matrix = [5,6,14,25; 14,55,44,16; 98,65,34,75; 67,89,21,88];
coord = [1,1; 1,3; 2,2; 3,2; 4,3; 4,4];
matrix_out = matrix; % Initialize matrix_out with the original matrix
for K = 1:length(coord)
    A = coord(K,:);
    A_x = A(1);
    A_y = A(2);
    matrix_out(A_x,A_y) = 0; % Update matrix_out with the value 0 at the specified coordinates
end
matrix_out
matrix_out = 4×4
     0     6     0    25
    14     0    44    16
    98     0    34    75
    67    89     0     0

By initializing `matrix_out` with `matrix` outside the loop, you ensure that it starts with the same values as `matrix`. Then, within the loop, you update the corresponding coordinates in `matrix_out` with the value `0`.

Hope this helps!