Finding sorted rows in a matrix
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Hi,
I need to know which rows of a matrix are sorted in ascending without using the "for" cycle. For instance, if i have:
outsx = [
1 1
2 1
3 1
1 2
2 2
3 2
1 3
2 3
3 3]
i want a vector containing indexes of which rows are sorted in ascending order. In this case.
ii= [1 4 5 7 8 9]
Thank you in advance
回答（3 个）
the cyclist
2021-3-20
For my current understanding of what you want, I believe this works:
ii = find(diff(outsx,[],2)>=0)
2 个评论
Jan
2021-3-20
I assume an all() is wanted:
ii = find(all(diff(outsx,[],2) >= 0, 2))
the cyclist
2021-3-21
Yes, thanks for catching that
outsx = [
1 1
2 1
3 1
1 2
2 2
3 2
1 3
2 3
3 3];
ii = find(outsx(:,2)>=outsx(:,1))
Star Strider
2021-3-20
Two approaches:
for k = 1:size(outsx,1)
TF(k,:) = issorted(outsx(k,:),2,'ascend')
end
Result = find(TF)
TF = outsx(:,2) >= outsx(:,1);
Result = find(TF)
both producing:
Result =
1
4
5
7
8
9
.
2 个评论
Marco Gaetani d'Aragona
2021-3-20
the cyclist
2021-3-20
FYI, just because code has a for loop does not necessarily mean it is slower than other solutions.
Finding a solution that works is the first step (partly to verify that the solution does what you want), and then thinking about readability and optimization follows.
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