I have to do some very repetitive calculations based on how many objects there are.
Example there are 4 objects.
Then I have to do these calculations:
1+2
1+3
1+4
2+1
2+3
2+4
3+1
3+2
3+4
4+1
4+2
4+3
1+3+2
1+4+3
1+2+4
3+2+1
3+4+2
3+2+4
4+2+1
4+3+1
4+2+3
1+2+3+4
How to do this in a non repetitive way of calculation all possibilities ? I want to calculate all possibilities expect that a object my not appear twice.
objs = [1, 2, 3, 4]
(1..objs.size).map {|i| objs.permutation(i).map {|o| o.reduce(:+) } }.flatten(1)
# => [
1, # 1
2, # 2
3, # 3
4, # 4
3, # 1+2
4, # 1+3
5, # 1+4
3, # 2+1
5, # 2+3
6, # 2+4
...
10, # 1+2+3+4
...
10 # 4+3+2+1
]
objs.combination(i) instead of a permutation. And map + flatten(1) -> flat_map (ruby 1.9). 2.upto(xs.size).flat_map { |n| xs.combination(n).map { |cs| cs.inject(:+) } }
You can look at Array.permutations
When invoked with a block, yield all permutations of length n of the elements of ary, then return the array itself. If n is not specified, yield all permutations of all elements. The implementation makes no guarantees about the order in which the permutations are yielded.
