Unique Function based on 2 columns [Instead of rows]

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

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

b=a{1}
c=b(:,3:4)
[~,idx]=unique(c,'rows','first','stable')
out=b(idx,:)

4 个评论

Thank you Azzi for the concise steps. However, it doesn't give the count of the number of duplicates. [In this case, 2,2,2 for each pair of duplicates]. Is there a way to count the number of duplicates?
There is certainly a simpler way, but if you add a 3rd output parameter to the call to UNIQUE
[~,idx,cnt] = unique(c, ... )
you can get effective counts with the following
>> cnt = accumarray(cnt, ones(size(cnt)))
cnt =
2
2
2
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!
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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