Operate by logical arrays element by element (error: Unable to perform assignment because the left and right sides have a different number of elements.)

Hi:

I have a problem using logical arrays. I'd like to use the array for matrix element operation, for example:

a=[1, nan];
b=[8, 9];

I want to replace all nan elements in matrix a and replace it with b. For this example, I want output is [1, 9].

I've tried the followings:

TF= isnan(a); %gives a logical array [0, 1]
a(TF)=b; 

or

a(isnan(a))=b;

Both give the error message "Unable to perform assignment because the left and right sides have a different number of elements."

if isnan(a)
a=b;
end

No error message, but all elements in matrix a won't change.

I wonder if there are any ways to do it avoid using for loops (works, but slower)

for i=1:2
    if isnan(a(i))
    a(i)=b(i);
    end
end

Thanks.

Answer 1

[Stephen23]

a = [1,nan];
b = [8,9];
x = isnan(a);
a(x) = b(x)

a = 1×2

1 9

[FFT]

Thank you very much!