Combining data with matching elements in the first two columns

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Muneer 2014-2-18

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https://ww2.mathworks.cn/matlabcentral/answers/116662-combining-data-with-matching-elements-in-the-first-two-columns

评论： Azzi Abdelmalek 2014-2-19

采纳的回答： the cyclist

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Hello, I have a data table that looks like this

381  784  0
381  0  21.4375
388  1703  0
388  0  4.109375
487  304  0
487  0  15.09375
506  1480  0
506  0  28.234375
520  454  0
520  0  40.21875

For all the entries where the first two columns match (ie, the first two rows), I would like to combine those two rows into one. So these two rows:

920  381  784  0
920  381  0  21.4375

Will become

920 381 784 21.4375

And so on for the rest of the data set. I would appreciate any help.

Thanks

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the cyclist 2014-2-18

Is that exact pattern guaranteed? Namely, will the first zero always be in column 4, and the second zero always be in column 3? And will there always be a pair of rows like that?

Muneer 2014-2-18

No it isn't guaranteed that there will always be a pair of rows. If there is one row with no matching row, however, it will have a value in column three, not column four. Thanks

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the cyclist 2014-2-18

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编辑：the cyclist 2014-2-19

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Here's one way:

[~,i,j]=unique(M(:,1:2),'rows');
[M(i,[1 2]),accumarray(j,M(:,3)),accumarray(j,M(:,4))]

where M is your original array.

EDIT: Original solution only gave the last two columns, so I fixed it to give all the columns you need.

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Azzi Abdelmalek 2014-2-18

This does not give the result

Azzi Abdelmalek 2014-2-19

The cyclist, your code doesn't work if there are more then two duplicate rows (I mean duplicate for the two first column).

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Azzi Abdelmalek 2014-2-18

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/116662-combining-data-with-matching-elements-in-the-first-two-columns#answer_124813

编辑：Azzi Abdelmalek 2014-2-18

在 MATLAB Online 中打开

M=[920  381  784  0
  920  381  0  21.4375
  23  388  1703  0
  23  388  0  4.109375
  445  487  304  0
  445  487  0  15.09375
  1100  506  1480  0
  1100  506  0  28.234375
  245  520  454  0
  245  520  0  40.21875]
[~,idx,jj]=unique(M(:,1:2),'rows','stable'); % M is your matrix
n=numel(idx)
out=zeros(n,size(M,2))
for k=1:n
  out(k,:)=max(M(find(jj==k),:))
end