All possible combination for picking up from arrays

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joy
joy 2014-10-14
评论： Guillaume 2014-10-14
I have 3 arrays namely a,b & c.
Now I have total 10 elements..a has 5 elements, b has 2 and c has 3, all elements in an array are identical.
I have to pick up 4 elements in all possible distinct combination from these arrays, like I can pick up all 4 from array a, again 3 from array a and 1 from array b , 2 from each array b & c and so on.
How to write this logic in matlab so that all possible combination is covered.

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Guillaume
Guillaume 2014-10-14
编辑：Guillaume 2014-10-14
One simple way that may be a bit wasteful as it calculate more combinations than necessary and remove redundant ones:
Concatenate your 3 arrays and use nchoosek to pick all combinations of 4 elements from that concatenation. Remove duplicate combinations using unique (with the 'rows' option).
With only ten elements it's near instananeous anyway. With moderately more elements, nchoosek will take too long and generate too many combinations, so a different method will have to be used.
  2 个评论
joy
joy 2014-10-14
Actually elements in the array are identical. so let array a contains 5 elements say a=[1,2,3,4,5]; now, If I select 1,2,3,4 or 2,3,4,5 it doesn't matter.
Guillaume
Guillaume 2014-10-14
Yes, I understood that the elements are identical. That's why you use unique to remove the combinations where the same number of elements have been picked from each array:
a = [1 1 1 1 1];
b = [2 2];
c = [3 3 3];
abc = [a b c];
allcombs = nchoosek(abc, 4);
combs = unique(allcombs, 'rows')

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