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Unique Function based on 2 columns [Instead of rows]

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RDG
RDG 2013-4-9
Suppose, I have a cell array, a, with contents as such:
a{1}=[1 3 4 5;
3 3 4 5;
5 5 4 5
2 4 2 6;
6 5 2 6
7 2 3 1;]
How can I apply the 'unique' function on 2 columns [column 3 and 4] such that they will return the value '3' and '2'. [Since there are 3 duplicates for the pair 4,5 and 2 duplicates for the pair 2,6.]
Solution proposed:
diff(find([true; any(diff(a{1}(:,3:4)),2); true]))
-----------------------------------------------------------------------
However, when the arrangement of the contents is changed, for eg.
a{1}=[ 1 3 4 5;
3 3 2 6;
5 5 4 5
2 4 3 1;
6 5 2 6
7 2 3 1;]
The code doesn't seem to identify the similarity/duplicated for column 3 and 4 [Corresponding rows: 1 & 3; 2 & 5; 4 & 6]
  1 个评论
Cedric
Cedric 2013-4-9
No, this code assumes blocks of similar rows (for cols 3 and 4), as it seems to be the case in your first example.

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2013-4-9
b=a{1}
c=b(:,3:4)
[~,idx]=unique(c,'rows','first','stable')
out=b(idx,:)
  4 个评论
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RDG
RDG 2013-4-9
This problem which I'm facing has exposed me to so many new commands in Matlab and logic which I never thought of before. Thank you for your great insight!
Cedric
Cedric 2013-4-9
编辑：Cedric 2013-4-9
Yep, in some sense it is easier to understand how to solve an ODE than to understand how to perform data manipulation efficiently ;-)

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