# Find differences in a set of points without a for loop

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Sonoma Rich on 21 Apr 2015
Commented: Image Analyst on 19 May 2022 at 12:14
I a vector of numbers that I am trying to find the differences between each element in the vector without a for loop. Below is a code example. Is there a more efficient way to execute this code without a for loop?
x = rand(20,1);
diff = zeros(length(x),length(x));
for ix = 1:length(x)
for iy = (ix+1):length(x)
diff(ix,iy) = abs(x(ix) - x(iy));
end
end

Image Analyst on 21 Apr 2015
Edited: Image Analyst on 21 Apr 2015
diff() is a built in function. Don't use it for a variable name.
For a microscopic length such as 20, don't worry about a for loop. It won't take any time at all, and in fact may take less than calling some fancy function.
Image Analyst on 21 Apr 2015
Richard's "Answer" moved here since it is not an answer to the original question:
Thanks for the help. My actual code has a vector that is much larger. I was just using this as an example.

Mehri Mehrnia on 19 May 2022 at 5:19
I have the question to find all pair-wise difference in a group without loop!
My array in scale of milions!
Image Analyst on 19 May 2022 at 12:14
Try using pdist2, pdist, or diff

Bruno Luong on 19 May 2022 at 6:34
Edited: Bruno Luong on 19 May 2022 at 9:07
x = randi(10,3,1)
x = 3×1
5 4 8
d = abs(x - x.')
d = 3×3
0 1 3 1 0 4 3 4 0