## summing along 3rd dimension every 10 frames

### Lucrezia Cester (view profile)

on 14 Nov 2019 at 19:29
Latest activity Commented on by the cyclist

### the cyclist (view profile)

on 14 Nov 2019 at 20:12

### Philippe Lebel (view profile)

Hello,
I have a matrix of 32x32x2500.
I would like to sum it along the third dimension so to have a matrix of 32x32x250 so that along the third dimesion i have summed 10 paged together thus increasing my SNR.
I have tried with something like
sumby10 = zeros(32,32,2500);
for a = 1:11:2500
sumby10(:,:,a) = sum(micron_59frames(:,:,a:a+9),3);
end
but this does not work as it return a matrix of 32x32x2500.

### Philippe Lebel (view profile)

on 14 Nov 2019 at 20:05

I would do:
sumby10 = zeros(32,32,250);
for a = 1:250
sumby10(:,:,a) = sum(micron_59frames(:,:,(a-1)*10+1:(a)*10),3);
end

### Stephan (view profile)

on 14 Nov 2019 at 19:59
Edited by Stephan

### Stephan (view profile)

on 14 Nov 2019 at 19:59

B = sum(reshape(A,32,32,10,[]),3);

### the cyclist (view profile)

on 14 Nov 2019 at 20:05
Edited by the cyclist

### the cyclist (view profile)

on 14 Nov 2019 at 20:07

Stephan provided a slick one-liner, but I think it might also be useful for you to see what mistakes you made. Here is a corrected version of your original code:
sumby10 = zeros(32,32,250);
for a = 1:250
idx = (a-1)*10+1:a*10;
sumby10(:,:,a) = sum(micron_59frames(:,:,idx),3);
end
Note a couple things that are different:
• I preallocated sumby10 to be only length 250 in dimension 3. Your preallocation guaranteed that your result would be the full 2500 in length
• I re-did the loop index. You were using the loop index "a" to write into "slices" 1,11,22,33 etc of the sumby10 matrix. You were leaving the in-between rows equal to zero -- but they were there.
• You were confusing the indexing of the old matrix (needed to span all 2500 rows) with indexing of the new matrix (only needs to span 250 rows)

Philippe Lebel

### Philippe Lebel (view profile)

on 14 Nov 2019 at 20:08
HaHA, i got you!
the cyclist

### the cyclist (view profile)

on 14 Nov 2019 at 20:12
¯\_(ツ)_/¯