How to order a matrix?

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Sky Scrapper
Sky Scrapper 2019-4-23
评论： Sky Scrapper 2019-4-23
Hello,
I have a matrix,
A=[ 100 5 0 ; 200 0 -5 ; 300 0 0 ; 300 5 0 ; -100 0 5 ; 300 0 0; 300 0 5];
I want to get,
A= [100 5 0; 200 0 -5 ; 300 0 0; 300 5 0 ; 300 0 5 ; -100 0 5];
I am writing code:
B= unique(A(:, 2:3),'rows');
then it's removing the first row as 5 0 is also repeted for the 4th row 300 5 0 but I need to keep the 1st row.
Is it possible to do?
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Adam
Adam 2019-4-23
It's not really obvious from your example what you are trying to achieve in a more general case. Your example just removes one row (which can be removed by using just a simple unique as mentioned) and then orders the remaining ones in a fairly unintuitive manner with respect to how they started.
What are you actually trying to keep? If you are trying to keep all unique rows then what I wrote works fine, if you are really trying to only run a unique on the 2nd and 3rd columns then your version does that, but from what you say, that isn't what you want to do.
Sky Scrapper
Sky Scrapper 2019-4-23
I could solve my problem. thanks for helping me!

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回答（2 个）

Alex Mcaulley
Alex Mcaulley 2019-4-23
编辑：Alex Mcaulley 2019-4-23
Try this:
[~,ia,~] = unique(A(:, 2:3),'rows','stable');
B = A(ia,:);
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Alex Mcaulley
Alex Mcaulley 2019-4-23
Using round
https://es.mathworks.com/help/matlab/ref/round.html
If you want to round the first column:
A = [ 100 5 0 ; 200 0 -5 ; 300 0 0 ; 300 5 0 ; -100 0 5 ; 300 0 0; 300 0 5];
A(:,1) = round(A(:,1),-2);
[~,ia,~] = unique(A(:, 2:3),'rows','stable');
B = A(ia,:);
Sky Scrapper
Sky Scrapper 2019-4-23
I have already done this. Again thanks a lot!

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Guillaume
Guillaume 2019-4-23
how can i do that?
Use uniquetol instead of unique. Note that the 'rows' option of unique is 'ByRows', true with uniquetol
[~, irows] = uniquetol(A(:, [2 3]), 'ByRows', true); %if you are happy with the default tolerance
B = A(irows, :);
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Sky Scrapper
Sky Scrapper 2019-4-23
Yes, i have already done that.
I had to take tolerance=0.02
Thank you very much for your kind support.

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