Ruby transform hash based on mapping

Question

Let's say I have a mapping of how I want a hash to turn out, along with new key names like this:

JSON_MAP = {
  image: {
    id: :id,
    media_url: :url,
    time: :duration,
    timestamp: :time_posted,
    text_caption: :caption,
    metadata: {
      camera: :camera_type,
      flash: :camera_flash
    }
  },
  viewers: {
    views: :view_count,
    likes: :likes_count
  }
}

and I have a hash like this:

{
  image: {
    id: 1,
    media_url: 'http://placekitten.com',
    nsfw: false,
    time: 4,
    timestamp: 14149292,
    text_caption: "I'm a kitten",
    metadata: {
      camera: 'iPhone',
      flash: true
    }
  },
  viewers: {
    views: 50,
    likes: 15
  },
  extras: {
    features: {
      enabled: true
    }
  }
}

I only want it to transform the data so it ends up like:

{
  image: {
    id: 1,
    url: 'http://placekitten.com',
    duration: 4,
    time_posted: 14149292,
    caption: "I'm a kitten",
    metadata: {
      camera: 'iPhone',
      flash: true
    }
  },
  viewers: {
    view_count: 50,
    likes_count: 15
  }
}

Basically, renaming all the keys based on the source map, and deleting any keys that don't match the source map...

You need to show your attempt to solve the problem. Merely showing us the desired data suggests you want us to write the code for you, which isn't what SO is for. Please read "How to Ask" including the linked pages. Also “How much research effort is expected of Stack Overflow users?” is useful. — the Tin Man
– the Tin Man, Commented Aug 12, 2016 at 23:15

Cary Swoveland · Accepted Answer · 2016-08-13 18:50:24Z

1

You can obtain your desired result using recursion.

def convert(mapper, hsh)
  mapper.each_with_object({}) do |(k,o),h|
    next unless hsh.key?(k)
    if o.is_a? Hash
      h[k] = convert(o, hsh[k])
    else
      h[o] = hsh[k]
    end
  end
end

Assuming h equals your second hash,

convert(JSON_MAP, h)    
  #=> { :image=>{
  #       :id=>1,
  #       :url=>"http://placekitten.com",
  #       :duration=>4,
  #       :time_posted=>14149292,
  #       :caption=>"I'm a kitten",
  #       :metadata=>{
  #         :camera_type=>"iPhone",
  #         :camera_flash=>true
  #       }
  #     },
  #     :viewers=>{
  #       :view_count=>50,
  #       :likes_count=>15
  #     }
  #   }

edited Aug 13, 2016 at 18:50

answered Aug 12, 2016 at 22:15

Cary Swoveland

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5 Comments

Daniel Jacob Archer Over a year ago

Hrm, that didn't work for me - saying "recurse" is not a method?

Cary Swoveland Over a year ago

I initially had two methods: convert and recurse, then realized I only needed one, convert, but I forgot to change recurse to convert in the body. I've made the correction.

Cary Swoveland Over a year ago

Please elaborate. The method works fine for the two hashes in your question.

Daniel Jacob Archer Over a year ago

Ah I found that it fails if a hash isn't there.. so if metadata didn't exist, it failed.

Cary Swoveland Over a year ago

Good catch. It would also fail if there were no key :image or :viewers. Your fix seems to cover all those cases.

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