Sum: every nth column and groups/blocks of columns
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Hi:
Is there any way to improve this code?
Thanks
Dominic
%
% Flows between sectors of countries
% 3 countries with 4 sectors
% Row and column headings are the same C1S1 C1S2 ......C4S3 C4S4
%
c=3; % no. of countries
s=4; % no. of sectors
X=magic(c*s); % 12
%
% add every 4th (sth) column of a matrix: 1,5,9 ... 4,8,12
% - result 12x4 (sum by sector)
%
S=sum(X(:,1:s:end),2); % 1:4:end
for k=2:s % 2:4
SS=sum(X(:,(k):s:end),2);
S=horzcat(S,SS);
end
%
% add columns in blocks of 4: 1-4, 5-8, 9-12 - result 12x3 (sum by country)
%
C=sum(X(:,[1:s]),2); % [1:4]
x=(s+1):s:(c*s); % 5:4:12
y=(2*s):s:(c*s); % 8:4:12
for k=[x;y]
CC=sum(X(:,[k(1):k(2)]),2);
C=horzcat(C,CC);
end
0 Comments
Accepted Answer
Bruno Luong
on 24 Aug 2022
Edited: Bruno Luong
on 24 Aug 2022
c=3; % no. of countries
s=4; % no. of sectors
X=magic(c*s); % 12
XX = reshape(X,size(X,1),s,[]);
S = sum(XX,3)
C = squeeze(sum(XX,2))
3 Comments
Bruno Luong
on 24 Aug 2022
Not only fewer line of code. It probably the fatest as it avoid matrix transposition.
More Answers (2)
Dyuman Joshi
on 24 Aug 2022
Edited: Dyuman Joshi
on 24 Aug 2022
%comment lines removed
c=3; % no. of countries
s=4; % no. of sectors
X=magic(c*s); % 12
Vectorized solution
S1=reshape(sum(reshape(X,[],c),2),[],s)
C1=reshape(sum(reshape(X',s,[])),[],c)
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