Applying function to a cell value

I have a code 

for k = 1:(length(dirlist))

img = imread([pathname, dirlist(k).name]);

flatImg = double(reshape(img,size(img,1)*size(img,2),size(img,3)));
idx = kmeans(flatImg,3); 
N{k}=(reshape(idx,size(img,1),size(img,2)))

end
save('final_result','N')

now i want to apply the follwing code to the N variable

y = diric(N,k),k=3

the size of N is 1x80

the values is 

   Columns 1 ..........Column80
      [256x256 double]    [256x256 double]