Asked by Hassan
on 22 Apr 2011

I have an array (10 rows,10 columns,5 bands) and wonder how I can convert the zero values to NaN. I used the following command line but it's not working. If I replace zero values with another value (like 2) it works but for an odd reason is not working with NaN. A(A==0)=NaN

I apperciate your help.

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Answer by John D'Errico
on 22 Apr 2011

Accepted answer

Given that your array is truly uint32, try this:

clear uint32(nan) ans = 0

NaNs are only defined in context of FLOATING point numbers.

Answer by John D'Errico
on 22 Apr 2011

It DOES work.

A = [1 2 0 -4 5 0 0 6]; A(A == 0) = NaN A = 1 2 NaN -4 5 NaN NaN 6

So you are mistaken that it fails. Very likely, you are failing to understand that matlab sometimes displays a number as 0, yet it is NOT zero.

format short A = [1 2 0.00000001 -4 5 0.000000023 0.000000000001 6] A = 1.0000 2.0000 0.0000 -4.0000 5.0000 0.0000 0.0000 6.0000

See that there are still three values that are displayed as zero, but the simple test for zero fails to see any of them

A == 0 ans = 0 0 0 0 0 0 0 0

I will also point out that you CANNOT test for a NaN using ==, as that test will always return false. This is easy to prove.

nan == nan ans = 0

The final possibility is that you have defined nan to be some other value. Thus

nan = 5;

Now I will not be able to assign something as a true nan, instead, matlab will use 5 when you try that. So, if you have defined nan = 0 someplace, then replacing zeros by nan will just insert zeros directly back in.

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John D'Errico
on 22 Apr 2011

Answer by Matt Fig
on 22 Apr 2011

Please do these three commands on your machine and paste the output, just like I did. Remember to use the {} Code button!

>> which nan built-in (C:\Program Files\MATLAB\R2007b\toolbox\matlab\elmat\nan) >> B = mod(1:5,2) B = 1 0 1 0 1 >> B(~B)=nan B = 1 NaN 1 NaN 1

.

. **EDIT**

Hassan, don't put in the >> when you run the code.

Answer by Ali Can ARIK
on 22 Apr 2011

Try this:

A(find(A==0)) = NaN;

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John D'Errico
on 22 Apr 2011

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