Join JSON with a common attribute - json

Question

I have a JSON with product items with a code, name and quantity. Sometimes items are duplicated (same code and name, different quantity). I'd like to sum the quantity of them in a single one.
Ex:
FROM
{ items: [{ code: 1, name: 'A', quantity: 2.0 }, { code: 1, name: 'A', quantity: 3.0 }, { code: 2, name: 'B', quantity: 4.0 }] }
TO
{ items: [{ code: 1, name: 'A', quantity: 5.0 }, { code: 2, name: 'B', quantity: 4.0 }] }

Answer 1

This should work:
items_hash = { items: [{ code: 1, name: 'A', quantity: 2.0 }, { code: 1, name: 'A', quantity: 3.0 }, { code: 2, name: 'B', quantity: 4.0 }] }
items_hash[:items] = items_hash[:items].each_with_object([]) do |item, collected_items|
if item_in_collected_items = collected_items.find { |i| i[:code] == item[:code] }
item_in_collected_items[:quantity] += item[:quantity]
else
collected_items << item
end
end
p items_hash
#=> { items: [{ code: 1, name: 'A', quantity: 5.0 }, { code: 2, name: 'B', quantity: 4.0 }] }

Answer 2

Code
def group_em(h)
h.transform_values do |a|
a.each_with_object({}) do |g,h|
h.update([g[:code], g[:name]]=>g) do |_,o,n|
g.merge(quantity: o[:quantity] + n[:quantity])
end
end.values
end
end
Examples
h = { items: [{ code: 1, name: 'A', quantity: 2.0 },
{ code: 1, name: 'A', quantity: 3.0 },
{ code: 2, name: 'B', quantity: 4.0 }] }
group_em(h)
#=> { items: [{ code: 1, name: 'A', quantity: 5.0 },
# { code: 2, name: 'B', quantity: 4.0 }] }
h = { items: [{ code: 1, name: 'A', quantity: 2.0 },
{ code: 1, name: 'A', quantity: 3.0 },
{ code: 1, name: 'C', quantity: 6.0 },
{ code: 2, name: 'B', quantity: 4.0 }] }
group_em(h)
#=> {:items=>[{:code=>1, :name=>"A", :quantity=>5.0},
# {:code=>1, :name=>"C", :quantity=>6.0},
# {:code=>2, :name=>"B", :quantity=>4.0}]}
h = { items: [{ code: 1, name: 'A', quantity: 2.0 },
{ code: 1, name: 'A', quantity: 3.0 },
{ code: 1, name: 'C', quantity: 6.0 },
{ code: 2, name: 'B', quantity: 4.0 }],
returns: [{ code: 2, name: 'B', quantity: 1.0 },
{ code: 1, name: 'A', quantity: 3.0 },
{ code: 1, name: 'C', quantity: 1.0 },
{ code: 2, name: 'B', quantity: 2.0 }]
}
group_em(h)
#=> {:items=>[{:code=>1, :name=>"A", :quantity=>5.0},
# {:code=>1, :name=>"C", :quantity=>6.0},
# {:code=>2, :name=>"B", :quantity=>4.0}],
# :returns=>[{:code=>2, :name=>"B", :quantity=>3.0},
# {:code=>1, :name=>"A", :quantity=>3.0},
# {:code=>1, :name=>"C", :quantity=>1.0}]}
Explanation
See Hash#transform_values, Enumerable#each_with_object, Hash#merge and the form of Hash#update (aka merge!) that employs a block to determine the values of keys that are present in both hashes being merged. Here that block is:
do |_,o,n|
g.merge(quantity: o[:quantity] + n[:quantity])
end
The values of the three block variables, _, o and n, are defined in the doc. I've used an underscore (a valid local variable) as the first variable--the common key--to signify that it is not used in the block calculation. That is common practice.
Note that:
h.update([g[:code], g[:name]]=>g)
is shorthand for:
h.update({ [g[:code], g[:name]]=>g })