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Asked by Tomas
on 11 May 2012

Hi, I have a matrix:

2 2 2 1 2 2 1 1 1 1 9 1 2 2 0 1

I need to pick rows that have same first number and sum them, but order of picking is important. In this case i need to pick first two rows and sum, then pick third and finaly fourth row; after that all the first numbers of column of new matrix should be the same depending on matrix sumed, so in the end there should be:

2 4 3 2 1 1 9 1 2 2 0 1

Any suggestions?

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Answer by Andrei Bobrov
on 12 May 2012

Accepted answer

I = cumsum([true;diff(a(:,1))~=0]); ii = fullfact(size(a)); out = accumarray([I(ii(:,1)), ii(:,2)],a(:))

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