使用Ruby中的循环创建深度嵌套的哈希

Question

I want to create a nested hash using four values type , name , year , value . ie, key of the first hash will be type , value will be another hash with key name , then value of that one will be another hash with key year and value as value .

The array of objects I'm iterating looks like this:

elements = [
    {
        year: '2018',
        items: [
            {
                name: 'name1',
                value: 'value1',
                type: 'type1',
            },
            {
                name: 'name2',
                value: 'value2',
                type: 'type2',
            },
        ]
    },
    {
        year: '2019',
        items: [
            {
                name: 'name3',
                value: 'value3',
                type: 'type2',
            },
            {
                name: 'name4',
                value: 'value4',
                type: 'type1',
            },
        ]
    }
]

And I'm getting all values together using two loops like this:

elements.each do |element|
    year = element.year
    element.items.each |item|
        name = item.name
        value = item.value
        type = item.type

        # TODO: create nested hash
    end
end

Expected output is like this:

{
    "type1" => {
        "name1" => {
            "2018" => "value1"
        },
        "name4" => {
            "2019" => "value4"
        }
    },
    "type2" => {
        "name2" => {
            "2018" => "value2"
        },
        "name3" => {
            "2019" => "value3"
        }
    }
}

I tried out some methods but it doesn't seems to work out as expected. How can I do this?

Answer 1

elements.each_with_object({}) { |g,h| g[:items].each { |f|
    h.update(f[:type]=>{ f[:name]=>{ g[:year]=>f[:value] } }) { |_,o,n| o.merge(n) } } }
  #=> {"type1"=>{"name1"=>{"2018"=>"value1"}, "name4"=>{"2019"=>"value4"}},
  #    "type2"=>{"name2"=>{"2018"=>"value2"}, "name3"=>{"2019"=>"value3"}}} 

This uses the form of Hash#update (aka merge! ) that employs a block (here { |_,o,n| o.merge(n) } to determine the values of keys that are present in both hashes being merged. See the doc for definitions of the three block variables (here _ , o and n ). Note that in performing o.merge(n) o and n will have no common keys, so a block is not needed for that operation.

Answer 2

Assuming you want to preserve the references (unlike in your desired output,) here you go:

elements = [
  {
    year: '2018',
    items: [
      {name: 'name1', value: 'value1', type: 'type1'},
      {name: 'name2', value: 'value2', type: 'type2'}
    ]
},
{
    year: '2019',
    items: [
      {name: 'name3', value: 'value3', type: 'type2'},
      {name: 'name4', value: 'value4', type: 'type1'}
    ]
  }
]

Just iterate over everything and reduce into the hash. On the structures of known shape is's a trivial task:

elements.each_with_object(
    Hash.new { |h, k| h[k] = Hash.new(&h.default_proc) } # for deep bury
) do |h, acc|
  h[:items].each do |item|
    acc[item[:type]][item[:name]][h[:year]] = item[:value]
  end
end

#⇒ {"type1"=>{"name1"=>{"2018"=>"value1"},
#             "name4"=>{"2019"=>"value4"}},
#   "type2"=>{"name2"=>{"2018"=>"value2"},
#             "name3"=>{"2019"=>"value3"}}}