MATLAB: Finding the index of spesific element in a matrix

indexmatrix

Lets say we have matrix:

a=[ 2, 3, 5

3, 4, 7

4, 4, 4] ;

I want to know index of a(4) which is the bold 3. This is just an example. I want to learn how to find index of a(n).

Best Answer

Assuming you want to index of the last match in the matrix:

Index=find(a==3,1,'last')

https://in.mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html - to know more

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MATLAB: An accumulating matrix to be reset when the limit value is reached, the value being reset must be moved to another matrix

This should do the trick. Note that you should use numel to count the number of elements, not length, which is just doing max(size(A)). The difference is usually nothing, but it will trip you up at some point.

B = [1, 4, 3, 1, 3, 2, 1, 0, 0, 1, 5, 6, 9, 1, 3];
A = cumsum (B);
C = zeros(size(A));
idx=find(A>=5);
while ~isempty(idx)
    idx=idx(1);
    C(idx)=A(idx);
    A(idx:end)=A(idx:end)-A(idx);
    
    idx=find(A>=5);
end
FormatSpec=[repmat('%d, ',1,numel(A)) '\n'];FormatSpec(end-3)='';
clc
fprintf(FormatSpec,A)
fprintf(FormatSpec,C)

Alternatively (which might be faster in some cases):

B = [1, 4, 3, 1, 3, 2, 1, 0, 0, 1, 5, 6, 9, 1, 3];
A = cumsum (B);
C = zeros(size(A));
idx=find(A>=5);
while ~isempty(idx)
    idx=idx(1);
    C(idx)=A(idx);
    A=A-A(idx);
    
    idx=find(A>=5);
end
A=cumsum(B)-cumsum(C);%restore real A

MATLAB: Find indices of one array in another array.

[~,idx]=setdiff(A,B,'rows');
idx_rows=setdiff(1:size(A,1),idx)

Best Answer

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MATLAB: An accumulating matrix to be reset when the limit value is reached, the value being reset must be moved to another matrix

MATLAB: Find indices of one array in another array.

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