How to retain only the rows of a matrix based on the unique numbers in the first column of the matrix?

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Mohammad Sayeed
Mohammad Sayeed 2014-4-22
评论： Mohammad Sayeed 2014-4-23
Hello guys Say that a=[1 3 3; 1 4 3; 2 4 3; 2 5 2; 2 4 2; 3 2 1; 4 3 4; 4 3 2] I need to keep the rows where I have only unique numbers in the first column of the matrix. That means I want to have this matrix a= [1 3 3; 2 4 3; 3 2 1; 4 3 4]. Or I also need to get [1 4 3; 2 4 2; 3 2 1; 4 3 2]. That means retaining the last unique row (based on only the first column) instead of the first. Are they possible? please help.
Kind regards
Sayeed

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2014-4-22
编辑：Azzi Abdelmalek 2014-4-22
[ii,jj,kk]=unique(a(:,1),'stable');
out1=a(jj,:)
out2=cell2mat(accumarray(kk,1:numel(kk),[],@(x) {a(max(x),:)}));
  1 个评论
Mohammad Sayeed
Mohammad Sayeed 2014-4-22
Dear Brother It was just perfect! Thank you very much for your kind solution. By applying your codes, I have got both the matrix that I was looking for. Thanks again.
Sayeed

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更多回答（1 个）

Andrei Bobrov
Andrei Bobrov 2014-4-22
编辑：Andrei Bobrov 2014-4-22
[~,b] = unique(a(:,1),'first');
out1 = a(b,:);
out2 = a([b(2:end)-1;size(a,1)],:);
or
[~,b1] = unique(a(:,1),'first');
[~,b2] = unique(a(:,1),'last');
out1 = a(b1,:);
out2 = a(b2,:);

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