Problem 42671. unique with nan

Created by Mehmet OZC

Solve Later

input

 x = [2 NaN 3 5 NaN;
      1 NaN 4 9 NaN;
      8 -2  7 6  -2;
      7  4  8 5  4];

output

 y_correct = 
 [2 NaN 3 5;
  1 NaN 4 9;
  8 -2  7 6;
  7  4  8 5];

Solve

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87 Solutions
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Last Solution submitted on Nov 27, 2025

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6 Comments

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Peng Liu on 23 Oct 2015

First test case is invalid. Please fix it.

Mehmet OZC on 24 Oct 2015

I have fixed it. Also rescored your score. Your solution is now correct.

Guillaume on 26 Oct 2015

A more complete description of what we're supposed to achieve would be useful. What are we supposed to do if a row has less elements than the others after applying unique? Pad it with zero as your second test seem to imply?

Peng Liu on 26 Oct 2015

The objective of the problem is to find unique columns in the matrix, performing like unique(A,'columns','stable'), but treating NaN as equal numbers.

Mehmet OZC on 27 Oct 2015

The explanation of Peng is correct. I inspired from the function of "isequalwithequalnans". You cannot use to test the equality of two arrays which contain nan values with the function of "isequal". The purpose is to write a function something like "uniquewithequalnans"

Guillaume on 27 Oct 2015

As standard unique does not operate on columns I didn't even realise that the example had two identical columns. I saw the problem as just remove the unique elements in each row which could potentially result in rows of different length. Hence my initial question.

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Problem 42671. unique with nan

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Problem 42671. unique with nan

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