Consolidating row values from previous column duplicate values.

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Willem
Willem 2013-8-1
Hi all,
Is it possible to write a script to make MATLAB look at the first two columns of a matrix, and if there are multiple rows where Column 1 and Column 2 have the same values, to put these rows together and sum the corresponding values of a third column.
An example would be like this;
[a x 2;
a x 3;
b x 4;
a y 5;
b y 6;
b y 7;
c y 8]
and so the script will recognize there are two rows with a in column 1 and x in column 2, so it will put them together and add the values in the third row.
So the output would be like this;
[a x 5;
b x 4;
a y 5;
b y 13;
c y 8]
Forgive my bad formatting of the matrix, but any help will be greatly appreciated!
Kind regards
Willem
  2 个评论
Evan
Evan 2013-8-1
编辑：Evan 2013-8-1
Do you only add rows that are adjacent to one another, or would another row, say [a x 6] appended to the bottom of the matrix, also be added to the top two?
Willem
Willem 2013-8-1
No, I have the ability to sort the data and make sure they will be sorted by the first two columns, with the primary sort being on the second column.

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采纳的回答

the cyclist
the cyclist 2013-8-1
编辑：the cyclist 2013-8-1
You need the accumarray function:
A = [1 1 3;
1 1 4;
1 1 7;
1 2 1;
1 2 6;
2 3 5;
3 6 4;
3 6 9;
3 6 3];
[Aunique,i,j] = unique(A(:,[1 2]),'rows');
Asum = accumarray(j,A(:,3),[],@sum);
output = [Aunique,Asum]
  5 个评论
显示 3更早的评论
Willem
Willem 2013-8-2
Thank you very much again, this is perfectly what I need. I will study and try to understand this code.
the cyclist
the cyclist 2013-8-2
Don't feel bad if accumarray seems confusing. It's doing a pretty complex thing, and I personally never found the documentation for that particular function to be helpful to me.

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更多回答（2 个）

Azzi Abdelmalek
Azzi Abdelmalek 2013-8-1
[a,b,c]=unique(A(:,1:2),'rows','stable')
out=[a accumarray(c,A(:,3))]
Andrei Bobrov
Andrei Bobrov 2013-8-2
编辑：Andrei Bobrov 2013-8-2
A = [1 1 3;
1 1 4;
1 1 7;
1 2 1;
1 2 6;
2 3 5;
3 6 4;
3 6 9;
3 6 3]
A(:,end + (1:3)) = randi(10,size(A,1),3);
[a1,ii,ii] = unique(A(:,1:2),'rows');
[i1 j1] = ndgrid(ii,1:size(A,2) - 2);
a2 = A(:,3:end);
out = [a1 accumarray([i1(:),j1(:)],a2(:))];

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