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Obtain every possible combination in array

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Tyler Murray
Tyler Murray el 30 de Mzo. de 2017
Comentada: Walter Roberson el 8 de Mayo de 2017
I have 3, 100 x 1 vectors that I am combining to make a m x 4 matrix. To obtain 4 columns in the desired output, two elements from the first vector are selected as the first two elements in a row, and then one element from the second vector as the third element, and one element from the third vector as the fourth element to complete the m x 4. I would like to get every possible row combination possible in one large matrix. I started with a huge nested for loop and quickly got lost and assume there must be a better way. Any help is appreciated.
  4 comentarios
Tyler Murray
Tyler Murray el 30 de Mzo. de 2017
By possible I mean row indices. Order does not matter I am just looking for the total number of combinations. Thus no permutations necessary. Thanks for your reply, I'd appreciate any help.
Kirby Fears
Kirby Fears el 30 de Mzo. de 2017
Editada: Kirby Fears el 30 de Mzo. de 2017
The combinations total to (100)*99/2*100*100 = 49,500,000 rows. It's probably worth rethinking this approach. I will post some code below anyway...

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Kirby Fears
Kirby Fears el 30 de Mzo. de 2017
Editada: Kirby Fears el 8 de Mayo de 2017
Here's a brute force generation of all combinations. Memory usage is more of a bottleneck than processing time, so I wrote it with for-loops.
Note that storing all combinations may not be the best approach to address your underlying use case.
Set sz = 100 to match your vector size; beware of 50 million rows.
% Setting up dummy data
sz = 10; % 4500 rows
a = (1:sz)';
b = a + sz;
c = b + sz;
res = NaN(sz^3*(sz-1)/2,4);
% Filling array with selections
iCounter = 0;
for ai = 1:(numel(a)-1),
for aj = (ai+1):numel(a),
for bi = 1:sz,
for ci = 1:sz,
iCounter = iCounter + 1;
res(iCounter,:) = [a(ai) a(aj) b(bi) c(ci)];
end
end
end
end
  2 comentarios
Ahmed Ibrahim
Ahmed Ibrahim el 7 de Mayo de 2017
If each element of vector with size (1,14) takes one value from this vector [0 0.625 1.25 2.5] . How can I obtain all possible combinations of this vector ?

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