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

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Glenn Roumen on 10 Jun 2013
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.

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)) ]
Glenn Roumen on 10 Jun 2013
Thank you very much!

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);