Question

I’ve got a ruby hash like this

[{user_id: 3, purchase: {amount: 2, type_id:3, name:"chocolate"},
 {user_id: 4, purchase: {amount: 1, type_id:3, name: "chocolate"},
 {user_id: 5, purchase: {amount: 10, type_id:4, name: "penny-candy"}]

I want to take the array and merge by the type_id, sum the amounts, connect the user to the amounts, so the end result would be

[{type_id: 3, name: "chocolate", total_amounts:3, user_purchases[{user_id:3, amount:2},user_id:4,amount:1}],
{type_id:4, name: "penny-candy", total_amounts: 10, [{user_id:5,amount:2}]}]

how would I go from one type of output to the other?

Answer 1

It’s a group_by problem. I’ll give you 2:

new_array = old_array.group_by{|x| x[:purchase][:type_id]}.values.map do |group|
  {:type_id => group[0][:purchase][:type_id], :total_amounts => group.map{|g| g[:purchase][:amount]}.reduce(&:+)}
end

and leave the other 2 as an exercise