How to switch the indexing order

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Maggie Chong 2023-6-15

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移动：VBBV 2023-6-15

In matlab, the indexing for the find function numbers the matrix from top to bottom. However, for my code I need to run left to right. For exampe [1 ,2,3] etc.

Is there a different function I can use to achieve this?

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VBBV 2023-6-15

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Use the transpose for your matrix and then apply find function to get the index for the actual matrix

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Answer 1

the cyclist 2023-6-15

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There's probably no way that isn't somewhat awkward, but here is a function that will convert a column-major index (which is what MATLAB uses) to a row-major linear index.

This assumes a 2-dimensional array, does no error checking, was untested on anything other than simple cases. (For example, didn't try empty arrays, etc.)

% Example use
% Some random matrix
M = rand(3,5);
% Use the function to find the 4th element in the first row, using row-major linear indexing
colMajorToRowMajor(4,M)
ans = 10
function rowMajorLinearIndex = colMajorToRowMajor(colMajorLinearIndex,M)
    
    % Get input size
    [MR,MC] = size(M);
    
    % Convert
    [cwr,cwc] = ind2sub([MC,MR],colMajorLinearIndex);
    rowMajorLinearIndex = sub2ind(fliplr([MC,MR]),cwc,cwr);
end