Removing rows that are not unique from an array?
显示 更早的评论
Is there an easy way to remove ALL rows that are NOT unique? For example, how would I get B from A?
A = [1 2; 1 3; 1 4; 1 2; 1 5];
B = [1 3; 1 4; 1 5];
I could do this in a loop, but there seems like there must be a more elegant way. I've looked at various applications in the forum using the unique() function, but a solution is not obvious to me.
Thanks!
采纳的回答
Star Strider
2017-7-7
This works:
A = [1 2; 1 3; 1 4; 1 2; 1 5];
[~,ia,ic] = unique(A, 'rows'); % Unique Elements
v = accumarray(ic, 1); % Tally Occurrences Of Rows
B = A(ia(v==1),:) % Keep Rows That Only Appear Once
B =
1 3
1 4
1 5
5 个评论
Andrei Bobrov
2017-7-7
编辑：Andrei Bobrov
2017-7-7
+1 (Vote)
Star Strider
2017-7-7
Thank you, Andrei!
Jan
2017-7-7
+1. It took me a while to understand, how to treat this as Run Length Encoding problem.
John Jendzurski
2017-7-8
Star Strider
2017-7-8
As always, my pleasure.
更多回答（1 个）
As = sortrows(A);
k = find([true; any(diff(As, 1, 1), 2); true]);
B = As(k(diff(k) == 1), :);
And if the original order is wanted:
[As, idx1] = sortrows(A);
k = find([true; any(diff(As, 1, 1), 2); true]);
idx2 = k(diff(k) == 1);
B = A(idx1(idx2), :);
For A = randi([1, 20], 1e5, 4) the first method is 15% faster than the unique/accumarray method.
3 个评论
John Jendzurski
2017-7-8
Image Analyst
2017-7-8
This is asked so often it should be in the FAQ. But before I do, I'd like to have a solution to the other case people ask a lot about, and that is where people want to keep the first instance of the duplicate row (along with unique rows), rather than toss out all rows that are members of duplicates. Another case might be to keep only the duplicate rows.
Isn't "keeping the first instance" solved by
unique(A, 'rows', 'first')
And for keeping the multiple occuring rows only use:
As = sortrows(A);
k = find([true; any(diff(As, 1, 1), 2); true]);
B = As(k(diff(k) > 1), :);
% ^ instead of ==
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