"fold" an array of hashes, recursion required? - ruby

Question

This is a simple example of my starting point :
[
{ 'drink' => [ 'hard', 'soft' ] },
{ 'hard' => [ 'beer', 'wine' ] },
{ 'soft' => [ 'water', 'orange_juice' ] },
{ 'food' => [ 'fruit', 'veg', 'meat' ] },
{ 'fruit' => [ 'apples', 'bananas', 'pears' ] }
{ 'veg' => [ 'cabbages', 'potatoes', 'carrots' ] },
{ 'potatoes' => [ 'king_edward', 'sweet', 'russet' ] }
]
I need to iterate over this, and "fold in" where the key to the values in a hash, is the value in another hash, so I end up with :
[
{ 'drink' => [ { 'hard' => [ 'beer', 'wine' ] }, { 'soft' => [ 'water', 'orange_juice' ] } ] },
{ 'food' => [ { 'fruit' => [ 'apples', 'bananas', 'pears' ] },
{ 'veg' => [ 'cabbages', { 'potatoes' => [ 'king_edward', 'sweet', 'russet' ] }, 'carrots' ] }
]
The nesting could be any level of depth, but the result will always end up being an array of hashes at its outermost ( if that makes sense ), with one or more hash in that array.
Edit: Or as suggested in comment below, the result structure could just be a hash, with 'drink', and 'food' keys pointing to the respective nested values in that hash. ( The items are not necessarily unique, two or more keys could point to the same value/s ).
I can iterate over an array and/or hash with ".each" etc., and apply logic and build the result structure iteratively, but I'm struggling with what I think is the recursive nature of this problem, in terms of making sure that everything that can be nested gets nested to any depth ( if that makes sense ).
I'm not looking for a complete solution, but just a mental nudge in the right direction as to how to go about creating a solution for this, because at the moment I keep venturing down dead-ends..

Answer 1

Edited: this updated solution is recursive as well, as the previous. I added some case in the input to show how can nest at a deepr level (beer for example)
def rec_map(to_map, collection, mapped)
if to_map.empty?
mapped
else
case to_map[0]
when String
current_key = to_map[0]
mapped_key = collection.find(-> {current_key}) { |item_hash| item_hash.has_key?(current_key) }
if current_key == mapped_key
rec_map(to_map[1..-1], collection, mapped << current_key)
else
with_mapped_values = Hash.new
mapped_values = rec_map(mapped_key[current_key], collection, [])
with_mapped_values[current_key] = mapped_values
rec_map(to_map[1..-1], collection, mapped << with_mapped_values)
end
when Hash
key = to_map[0].keys.first
values = to_map[0].values.flatten
with_mapped_values = Hash.new
mapped_values = rec_map(values, collection, [])
with_mapped_values[key] = mapped_values
rec_map(to_map[1..-1], collection, mapped << with_mapped_values)
else
raise "Not supported given #{to_map[0].class} expected String or Hash"
end
end
end
def key_has_match(key, collection)
if collection.empty?
return false
else
case collection[0]
when String
key == collection[0] || key_has_match(key, collection[1..-1])
when Hash
key_has_match(key, collection[0].values.flatten) ||
key_has_match(key, collection[1..-1])
else
raise "Not supported given #{collection[0].class} expected String or Hash"
end
end
end
def rec_fold(to_fold, collection, folded)
if to_fold.empty?
folded
else
key = to_fold[0].keys.first
if key_has_match(key, collection)
rec_fold(to_fold[1..-1], collection, folded)
else
with_mapped_values = Hash.new
values = to_fold[0][key]
with_mapped_values[key] = rec_map(values, collection, [])
rec_fold(to_fold[1..-1], collection, folded << with_mapped_values)
end
end
end
if $PROGRAM_NAME == __FILE__
original = [
{ 'drink' => [ 'hard', 'soft' ] },
{ 'hard' => [ 'beer', 'wine' ] },
{ 'beer' => [ 'lager', 'stout', 'ale' ] },
{ 'lager' => [ 'draught', 'bottle' ] },
{ 'draught' => [ 'pint', 'half' ] },
{ 'soft' => [ {'water' => ['tap', 'bottle']}, 'orange_juice' ] },
{ 'food' => [ 'fruit', 'veg', 'meat' ] },
{ 'fruit' => [ 'apples', 'bananas', {'pears'=> ['anjou', 'bartlett', 'concorde']} ] },
{ 'veg' => [ 'cabbages', 'potatoes', 'carrots' ] },
{ 'potatoes' => [ 'king_edward', 'sweet', 'russet' ] },
{ 'sweet' => [ 'red', 'brown', 'white' ] },
{'bottle' => ['green', 'red', 'blue']},
{'bartlett' => ['Woven baskets', 'Bags', 'Modified atmosphere']}
]
pp rec_fold(original, original, [])
end
# [{"drink"=>
# [{"hard"=>
# [{"beer"=>
# [{"lager"=>
# [{"draught"=>["pint", "half"]},
# {"bottle"=>["green", "red", "blue"]}]},
# "stout",
# "ale"]},
# "wine"]},
# {"soft"=>
# [{"water"=>["tap", {"bottle"=>["green", "red", "blue"]}]},
# "orange_juice"]}]},
# {"food"=>
# [{"fruit"=>
# ["apples",
# "bananas",
# {"pears"=>
# ["anjou",
# {"bartlett"=>["Woven baskets", "Bags", "Modified atmosphere"]},
# "concorde"]}]},
# {"veg"=>
# ["cabbages",
# {"potatoes"=>
# ["king_edward", {"sweet"=>["red", "brown", "white"]}, "russet"]},
# "carrots"]},
# "meat"]}]