How do I keep the hash associations when building permutations - ruby

Question

UPDATE: Possible solution at the end, but certainly not performant or ideal.
I created the following method that gives me close to what I want.
def multi_permutations(collection)
case collection.length
when 1
return collection.shift[1]
when 0
raise "You must pass in a multidimensional collection."
end
a = collection.shift[1]
b = multi_permutations(collection)
return_value = []
a.each do |a_value|
b.each do |b_value|
return_value << [a_value] + [b_value]
end
end
return return_value
end
When I pass in a hash with nested arrays that looks like this...
my_collection["item_9"] = [152]
my_collection["item_2"] = [139, 143, 145]
my_collection["item_13"] = [138, 142, 150]
my_collection["item_72"] = [137, 149, 151, 154]
my_collection["item_125"] = [140, 141]
my_collection["item_10"] = [144, 146, 147, 148, 153]
I want it to create an array of hashes with all permutations that looks like this...
[{ "item_9": 152 }, { "item_2": 139 }, { "item_13": 138 }, { "item_72": 137 }, { "item_125": 140 }, { "item_10": 144 }]
[{ "item_9": 152 }, { "item_2": 139 }, { "item_13": 138 }, { "item_72": 137 }, { "item_125": 140 }, { "item_10": 146 }]
[{ "item_9": 152 }, { "item_2": 139 }, { "item_13": 138 }, { "item_72": 137 }, { "item_125": 140 }, { "item_10": 147 }]
[{ "item_9": 152 }, { "item_2": 139 }, { "item_13": 138 }, { "item_72": 137 }, { "item_125": 140 }, { "item_10": 148 }]
[{ "item_9": 152 }, { "item_2": 139 }, { "item_13": 138 }, { "item_72": 137 }, { "item_125": 140 }, { "item_10": 153 }]
.
.
.
[{ "item_9": 152 }, { "item_2": 145 }, { "item_13": 150 }, { "item_72": 154 }, { "item_125": 141 }, { "item_10": 144 }]
[{ "item_9": 152 }, { "item_2": 145 }, { "item_13": 150 }, { "item_72": 154 }, { "item_125": 141 }, { "item_10": 146 }]
[{ "item_9": 152 }, { "item_2": 145 }, { "item_13": 150 }, { "item_72": 154 }, { "item_125": 141 }, { "item_10": 147 }]
[{ "item_9": 152 }, { "item_2": 145 }, { "item_13": 150 }, { "item_72": 154 }, { "item_125": 141 }, { "item_10": 148 }]
[{ "item_9": 152 }, { "item_2": 145 }, { "item_13": 150 }, { "item_72": 154 }, { "item_125": 141 }, { "item_10": 153 }]
What this function ends up doing is close but I lose the relationships.
[152, [139, [138, [137, [140, 144]]]]]
[152, [139, [138, [137, [140, 146]]]]]
[152, [139, [138, [137, [140, 147]]]]]
[152, [139, [138, [137, [140, 148]]]]]
[152, [139, [138, [137, [140, 153]]]]]
.
.
.
[152, [145, [150, [154, [141, 144]]]]]
[152, [145, [150, [154, [141, 146]]]]]
[152, [145, [150, [154, [141, 147]]]]]
[152, [145, [150, [154, [141, 148]]]]]
[152, [145, [150, [154, [141, 153]]]]]
The relationships are very important to me. The reason is, I plan to hydrate an object where the attrs are the keys in the hash. I'm sure this can be done in a better way, and I'm open to suggestions.
So one possible solution I've come up with is to create a keys array then flatten the permutations and zip them together in a hash.
results = []
permutations = multi_permutations(possibilities)
permutations.each do |permutation|
results << Hash[keys.zip permutation.flatten!]
end
This ends up giving me...
{"item_9"=>152, "item_2"=>145, "item_13"=>150, "item_72"=>154, "item_125"=>141, "item_10"=>146}
{"item_9"=>152, "item_2"=>145, "item_13"=>150, "item_72"=>154, "item_125"=>141, "item_10"=>147}
{"item_9"=>152, "item_2"=>145, "item_13"=>150, "item_72"=>154, "item_125"=>141, "item_10"=>148}
{"item_9"=>152, "item_2"=>145, "item_13"=>150, "item_72"=>154, "item_125"=>141, "item_10"=>153}

Answer 1

I couldn't get your solution to run because you did not provide how to call it, so I couldn't compare the efficiency.
What do you think about this solution? (the single argument has to be a Hash of Arrays, just like your my_collection)
my_collection = {}
my_collection["item_9"] = [152]
my_collection["item_2"] = [139, 143, 145]
my_collection["item_13"] = [138, 142, 150]
my_collection["item_72"] = [137, 149, 151, 154]
my_collection["item_125"] = [140, 141]
my_collection["item_10"] = [144, 146, 147, 148, 153]
def permutations!(input)
input.each do |key, possibilities|
possibilities.map!{|p| {key => p} }
end
digits = input.keys.map!{|key| input[key] }
digits.shift.product(*digits)
end
results = permutations!(my_collection)
Please notice that this method modifies the input object because of the map! usage.