Removing rows that are not unique from an array?

22 次查看（过去 30 天）
John Jendzurski
John Jendzurski 2017-7-7
编辑： Jan 2017-7-8
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!

请先登录，再回答此问题。

采纳的回答

Star Strider
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
显示 3更早的评论
John Jendzurski
John Jendzurski 2017-7-8
Thank you, Star Strider. This looks perfect. I was not aware of the accumarray() function...until now!

请先登录，再进行评论。

更多回答（1 个）

Jan
Jan 2017-7-7
编辑：Jan 2017-7-8
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
显示 1更早的评论
Image Analyst
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.
Jan
Jan 2017-7-8
编辑：Jan 2017-7-8
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 ==

请先登录，再进行评论。

类别

在 Help Center 和 File Exchange 中查找有关 Startup and Shutdown 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by