How can I subtract columns for each row by using a for loop
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Hi,
I have a matrix like this:
[1.011 1.004 1.054
1.008 0.998 1.042
0.984 0.988 1.024
1.026 1.006 1.016
1.000 0.996 0.977]
I would like to subtract each column for each row and store these results in a new matrix. How can I do this?
Thanks!
2 Comments
Joseph Cheng
on 29 Sep 2014
can you expand on what you mean by subtract each column for each row? I do not understand what you're subtracting with.
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More Answers (3)
Joseph Cheng
on 29 Sep 2014
Edited: Joseph Cheng
on 29 Sep 2014
you can use combnk() or nchoosek to determine the combination of column subtraction and perform a for loop for each combination.
X = randi(10,4,3);
combin = combnk(1:size(X,2),2);
for ind = 1:size(X,2)
newX(:,ind) = X(:,combin(ind,1))-X(:,combin(ind,2));
end
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Guillaume
on 29 Sep 2014
Use nchoosek to get all possible combinations of columns, and use that to calculate your differences:
m = [1.011 1.004 1.054
1.008 0.998 1.042
0.984 0.988 1.024
1.026 1.006 1.016
1.000 0.996 0.977];
colcomb = nchoosek(1:size(m, 2), 2);
coldiff = zeros(size(m, 1), size(colcomb, 1));
for comb = 1:size(colcomb, 1)
coldiff(:, comb) = diff(m(:, colcomb(comb, :)), 1, 2);
end
7 Comments
dpb
on 29 Sep 2014
For what working definition of small? But, basic idea is one of two choices...
a) go ahead and generate all pairs and then compute the comparison statistic and choose the N smallest of those, or,
b) compute each pair and the statistic at same time; after N replace the largest of those kept with the last if new is less; update the maxValue comparison value.
Andrei Bobrov
on 30 Sep 2014
Edited: Andrei Bobrov
on 30 Sep 2014
X = [1.011 1.004 1.054
1.008 0.998 1.042
0.984 0.988 1.024
1.026 1.006 1.016
1.000 0.996 0.977];
n = nchoosek(1:size(X,2),2);
out = squeeze(diff(reshape(X(:,n'),[],2,3),1,2));
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