For loop not stopping

Hi! I have a raster file in tiff format which has some values set to -9999. I wrote a small code that should replace all -9999 values with NaN. Whren I execute the code the loop just keeps on going and it wont stop and generate the result. Can you please hel me figure out why? I am not attaching the raster because it is to big.

%reading  Raster Input data from a file 
[aspect, A] =readgeoraster('Aspect_0,5m.tif');
[slope, A] = readgeoraster('Slope_0,5m.tif')

imagesc(aspect)

%reading  csv Input data from a file 
discontinuity_orientations =readtable('orientations.xlsx') ;

for i =1:size(aspect,1)
if aspect (i,1)==-9999
   aspect (i,1) = NaN
end
end

Answer 1

[David Hill]

Instead of a for-loop, just do it all at once.

idx=aspect(:,1)==-9999;
aspect(idx,1)=nan;

[Hrvoje Lukacic]

Thank you for your answer !! But just in case, how to I make a for loop which goes from element to element and does some operation?

Answer 2

[VBBV]

if ismember(-9999,aspect(i,1))

Check using ismember