How to turn values in one matrix corresponding to a specific element in another into NaN

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Alexander Engman 2018-4-19

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Hi!

If I have two matrices:

A=[1 2 NaN; 4 NaN 6; NaN 8 9]
B=[11 12 13; 14 15 16; 17 18 19]

And I want to turn the elements in B corresponding to the elements that are NaN in A also into NaN, how would I do it? Basically the end result I want is:

A=[1 2 NaN; 4 NaN 6; NaN 8 9]
B=[11 12 NaN; 14 NaN 16; 17 NaN 19]

But my matrices are a lot bigger and I need a systematic approach.

Thanks in advance!

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Bob Thompson 2018-4-19

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nanarray = isnan(A);
B(nanarray==1) = NaN;

Did you mean to have the B(3,2)=NaN instead of B(3,1)?

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Guillaume 2018-4-19

Well, the thing is that nanarray==1 returns the exact same logical array you started with.

Bob Thompson 2018-4-19

Yes, and thinking about it in greater detail I can see how. The challenge for me when indexing in matlab is that I am a very visual person, and a lot of times with the logic indexing I don't take the time to look at every in between step, so I don't automatically know exactly what is happening. Therefore, in favor of being safe I tend to unintentionally build redundancies into my code to make sure it works. It's a dangerous habit, but one I simply haven't been coding long enough to break.

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