How to create a matrix out of all the possible combinations of a vector
조회 수: 13 (최근 30일)
이전 댓글 표시
Hi !
I want to fill a vector with specifice numbers of 1's and -1's, and the rest are zeros. And get all possible combinations in each row of a matrix.
For example, if I have a vector of length 12 and I want to have 5 elements = +1 and 4 elements = -1
Then, the results should be like:
M=[1 1 1 1 1 -1 -1 -1 -1 0 0 0; 0 0 0 1 1 1 1 1 -1 -1 -1 -1; -1 1 1 1 1 1 -1 -1 -1 0 0 0; .....]
and every other distinct combination of the three numbers.
댓글 수: 0
채택된 답변
Andrei Bobrov
2019년 7월 23일
편집: Andrei Bobrov
2019년 7월 23일
In your case:
a = 3:5;
v = [0,-1,1];
n = cumsum(a,'reverse');
C1 = nchoosek(1:n(1),a(1)); % Here are the two calls on 'nchoosek'
C2 = nchoosek(1:n(2),a(2));
M = ones(size(C1,1)*size(C2,1),n(1)); % First, fill M with all 1's
k1 = 0;
for k2 = 1:size(C1,1)
p1 = C1(k2,:); % Use C1 to generate indices for inserting 0's
q1 = 1:n(1);
q1(p1) = []; % These indices will point to -1 and 1 locations
for k3 = 1:size(C2,1)
p2 = C2(k3,:); % Use C2 to generate indices for inserting -1's
k1 = k1 + 1; % Advance the row index of M
M(k1,p1) = v(1); % Insert 0's
M(k1,q1(p2)) = v(2); % and -1's
end
end
댓글 수: 2
Rik
2019년 7월 23일
Just out of curiosity (and because I can't test myself because I'm on mobile): does this code allow longer vectors? And if so, why? What makes this approach fundamentally different from perms()?
추가 답변 (1개)
Rik
2019년 7월 23일
https://www.mathworks.com/help/matlab/ref/perms.html
댓글 수: 2
Rik
2019년 7월 23일
All combinations will result in a huge matrix if you have a large number of elements. As the documentation warns: this is only practical for a small number of elements. This is a fundamental problem that you need to solve separately.
참고 항목
카테고리
Help Center 및 File Exchange에서 Matrices and Arrays에 대해 자세히 알아보기
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!