comparing matrix elements and performing operation if equal

Question

Mahi Nazir 2013-11-14

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/106095-comparing-matrix-elements-and-performing-operation-if-equal

编辑： N/A 2019-7-5

采纳的回答： Simon

在 MATLAB Online 中打开

If I have a matrix

A=

I want to scan through the matrix and when ever the first column elements are equal, the 3rd column elements should get added up

e.g: the resultant matrix should be

18 18 1

17 20 2

18 18 2

17 25 4

19 16 3

18 18 3

19 17 6

Please help me in this

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N/A 2019-7-5

编辑：N/A 2019-7-5

My problem is also the same i just have one little extension that whenever the elemnts in column 1 and 3 both are repeated elsewhere in matrix then only third column should get added up

e.g

A=

18 18 1

17 20 2

18 18 1

17 25 2

19 17 3

18 18 1

19 17 3

then answer should be

18 18 1

17 20 2

18 18 2

17 25 2

19 17 3

18 18 3

19 17 6

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Answer 1

Simon 2013-11-14

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https://ww2.mathworks.cn/matlabcentral/answers/106095-comparing-matrix-elements-and-performing-operation-if-equal#answer_115177

编辑：Simon 2013-11-14

在 MATLAB Online 中打开

Hi!

% get indices of unique values
[~, ~, c] = unique(A(:, 1));
% loop over all unique values
for n = 1:max(c)
   ind = n==c;
    % cumulative sum
    cs = cumsum(A(ind, 3));
    % set third column
    A(ind, 3) = cs;
end