3D array index as the element itself?

[Temp Orary]

I'm a user using octave not on a daily basis but only sparcely. Something 
came up to me that I believe is very easy to vectorize (if you are a 
frequent user of octave) but it's not so obvious to me. So here it is:

for i=1:3
 for j=1:3
   for k=1:3
     r(i,j,k, 1)=i;
     r(i,j,k, 2)=j;
     r(i,j,k, 3)=k;
   endfor
 endfor
endfor

Namely, in 3D grid space, r(i,j,k, 1) extracts and assigns to itself the 
x-axis index, r(i,j,k, 2) the y-axis index, and so forth. 

First I thought it'd be very easy to convert this loop into one vectorized 
expression, but now it's just confusing. For 3x3x3 loop, this is not a 
problem but when it becomes something like 512x512x512, this loop seems to 
take forever. Any idea, friends?

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