Problem 42671. unique with nan

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Solution 767165

Submitted on 26 Oct 2015

Size: 20
Leading solution size is 21.

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Guillaume on 2 Nov 2015

An easy way to defeat that solution would be to use proper floating point numbers in the test suite. x = pi is enough to make it fail.

Mehmet OZC on 3 Nov 2015

Yes, indeed. I have added test cases and rescored all solutions. Some of them failed.

Peng Liu on 3 Nov 2015

Don't you think this is just a matter of the common round-off error for floating point numbers? Indeed, people rarely use exact equality == for floating-point numbers, which is probably why MATHWORKS has introduced uniquetol, as opposed to unique, to determine unique floating point numbers WITHIN TOLERANCE. If you insist exact equality must be used here, there are many workarounds anyway... My new solution is one of the examples.

Guillaume on 4 Nov 2015

No, this has nothing to do with round-off error. The solution itself rounds massively the input. If I pass x = pi to unique, I expect pi as an output, not 3.1416.

Peng Liu on 4 Nov 2015

I should have been more careful with my wording. I meant that the issue you pointed out is due to "rounding" of num2str. num2str(pi) rounds pi to 3.1416. To remedy this, you can increase the default precision of num2str using its 2nd input parameter. For instance, num2str(x,20) should work for all floating point numbers including pi. This can be checked as follows: >> x = [pi,rand(1,10),Inf,NaN,sqrt(2)]; >> isequaln(str2num(num2str(x,20)),x)

Test Suite

Test	Status	Code Input and Output
1	Pass	%% x = [2 NaN 3 5 NaN; 1 NaN 4 9 NaN; 8 -2 7 6 -2; 7 4 8 5 4];; y_correct = [2 NaN 3 5; 1 NaN 4 9; 8 -2 7 6; 7 4 8 5]; assert(isequalwithequalnans(unique_with_nan(x),y_correct))
2	Pass	%% x = [1 0 0 1;NaN 1 0 NaN;NaN 0 1 NaN;0 0 0 0]; y_correct = [1 0 0;NaN 1 0;NaN 0 1;0 0 0]; assert(isequalwithequalnans(unique_with_nan(x),y_correct))
3	Pass	%% x = [1 0 1 1 1 1 0;0 1 1 1 1 1 0;0 0 NaN NaN NaN NaN 0;0 0 NaN NaN NaN NaN 0;0 0 NaN NaN NaN NaN 0;0 0 0 0 0 0 0;0 0 0 0 0 0 1]; y_correct = [1 0 1 0;0 1 1 0;0 0 NaN 0;0 0 NaN 0;0 0 NaN 0;0 0 0 0;0 0 0 1]; assert(isequalwithequalnans(unique_with_nan(x),y_correct))
4	Fail	%% x = [2 NaN 3 5 NaN; 1 NaN 4 9 NaN; 8 pi 7 6 pi; 7 eps 8 5 eps]; y_correct = [2 NaN 3 5; 1 NaN 4 9; 8 pi 7 6; 7 eps 8 5]; assert(isequalwithequalnans(unique_with_nan(x),y_correct)) Assertion failed.

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Problem 42671. unique with nan

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