MATLAB Answers


convert zeros to nan

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.


Log in to comment.



No products are associated with this question.

4 Answers

Answer by John D'Errico on 22 Apr 2011
 Accepted Answer

Given that your array is truly uint32, try this:

ans =

NaNs are only defined in context of FLOATING point numbers.

  1 Comment

I tried that. I got the same answer (ans=0).

Log in to comment.

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 =

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.


I think Sean has the answer. Are you using some other class? If you don't give us sufficient information, we are just guessing here.

Nan is not defined as a valid value for uint32 numbers.

OK, in that case I need to use other values instead of NaN. thanks John for the help.

Log in to comment.

Answer by Loginatorist 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



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


thanks Matt for the comment. it gives me the following error:
??? built-in (C:\Program Files\MATLAB\R2007b\toolbox\matlab\elmat\nan)
Error: Unexpected MATLAB operator.

I hope you didn't try to put in the >> when you did the commands, did you?? I only left them there to show that I did this at the command window!

No I didn't. I am using Matlab 2009b version on the university network. i couldn't find Matlab folder in Program Files.

Log in to comment.

Answer by Ali Can ARIK on 22 Apr 2011

Try this:

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


Show 1 older comment

What does it do when you try that? Have you possibly defined a variable nan to have some other value?

I clear all variables using 'clear all' command. it can't convert zeros to nan for no reason.

when I convert a value to NaN, it is converted to zero.

Log in to comment.

Discover MakerZone

MATLAB and Simulink resources for Arduino, LEGO, and Raspberry Pi

Learn more

Discover what MATLAB® can do for your career.

Opportunities for recent engineering grads.

Apply Today

MATLAB Academy

New to MATLAB?

Learn MATLAB today!