How do I average rows which contain the same first to elements?

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I'm stuck on this problem for a while. I want to obtain a matrix which is averaged for the rows which contain the same first two elements. I don't want to clear the rows which are not equal for the first two elements. When I have a matrix A:
A=[1 1 1 1 1
1 2 3 4 5
1 2 4 4 4
1 2 3 3 3
2 2 2 2 2
2 2 3 3 3]
I want the outcome to be:
A=[1 1 1 1 1
1 2 3.33 3.67 4
2 2 2.5 2.5 2.5]
I hope someone could help me on this.

Accepted Answer

Ahmed
Ahmed on 10 Jun 2013
This solution is not very elegant, but should work. There is room for improvement, though.
uA = unique(A(:,1:2),'rows');
A = [uA cell2mat(cellfun(@(x)...
mean(A(all(bsxfun(@eq,A(:,1:2),x),2),3:end),1), ...
num2cell(uA,2),...
'UniformOutput',false)) ]

More Answers (1)

Andrei Bobrov
Andrei Bobrov on 10 Jun 2013
Edited: Andrei Bobrov on 10 Jun 2013
[~,~,c] = unique(A(:,1:2),'rows');
out = accumarray([repmat(c,size(A,2),1) kron((1:size(A,2))',...
ones(size(A,1),1))],A(:),[],@mean);
or
[c c c] = unique(A(:,1:2),'rows');
[ii,jj] = ndgrid(c,1:size(A,2));
out = accumarray([ii(:) jj(:)],A(:),[],@mean);

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