How to collapse within a column vector

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Ara Jo
Ara Jo on 17 Jul 2020
Commented: Ara Jo on 18 Jul 2020
Hello,
I am trying to collapse a long column to a shorter one by suming across elements. For instance, if I have:
x =
1
2
3
4
5
6
7
8
9
I would like to sum up every three elements and arrive at:
y= 6
15
24
This is basically the 'collapse' function in Stata but I'm struggling to do it in Matlab. Thanks for your advide.

Accepted Answer

Arthur Roué
Arthur Roué on 17 Jul 2020
Edited: Arthur Roué on 17 Jul 2020
You can use the sum function after reshape your vector into a matrix
vX = 1:9;
Interval = 3;
mX = reshape(vX, Interval, numel(vX)/Interval)
mX =
1 4 7
2 5 8
3 6 9
sum(mX)
ans =
6 15 24
/!\ reshape() won't work if the number of elements in vX is not a multiple of Interval
  4 Comments
Ara Jo
Ara Jo on 18 Jul 2020
Works perfectly - thank you very much!

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More Answers (1)

Alan Stevens
Alan Stevens on 17 Jul 2020
One possibility is:
x = 1:12;
for i = 1:length(x)/3
p = 3*(i-1)+1;
y(i) = sum(x(p:p+2));
end

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