Strange results from unique

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David Winthrop
David Winthrop on 27 May 2021
Edited: David Winthrop on 27 May 2021
I recently encountered a strange result that defies explanation. I took a screenshot. How can this be?
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the cyclist
the cyclist on 27 May 2021
It's always better to upload the data and code, rather than an image (which we cannot work with).
Yes, someone might be able to eyeball what is going on, but usually not.

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Accepted Answer

Walter Roberson
Walter Roberson on 27 May 2021
XLv{1} is a vector of 702 elements, YLv{1} is a vector of 702 elements. When you combine them you get 702 unique rows. But that does not imply that there are no duplicates amongst Xlv{1] or YLv{1} .
1 3
1 4
2 3
2 4
4 unique rows, right?
Now let XLvs be [1 2] and YLvs be [3 4]. ismember([1 1 2 2], [1 2]) would be [true true true true], ismember([3 4 3 4], [3 4]) would be [true true true true]. & the two of them to get [true true true true], which has a sum of 4... even though there are only 2 unique values in each of XLvs and YLvs.
  1 Comment
David Winthrop
David Winthrop on 27 May 2021
Edited: David Winthrop on 27 May 2021
Ah, I see that what I really wanted, since these are coordinate sets, is:
ismember([Xlv{1},Ylv{1}],[XLvs,YLvs],'rows')
This gives the expected result of length 85.
Thanks! I did not know ismember could match rows that way.

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