How can I subtract columns for each row by using a for loop
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Jimmy
el 29 de Sept. de 2014
Editada: Andrei Bobrov
el 30 de Sept. de 2014
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 comentarios
Joseph Cheng
el 29 de Sept. de 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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Más respuestas (3)
Joseph Cheng
el 29 de Sept. de 2014
Editada: Joseph Cheng
el 29 de Sept. de 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
el 29 de Sept. de 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 comentarios
dpb
el 29 de Sept. de 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
el 30 de Sept. de 2014
Editada: Andrei Bobrov
el 30 de Sept. de 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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