JavaScript - tool to restructure list of objects?

Question

This is a data-structurey kind of question, so I thought this would be a good forum to ask it in. I'm starting to run into the issue below quite a bit. Some service sends me data in the format below. It's an array of people, that tells me what pets they own.

owners = [
  {
    owner: 'anne',
    pets: ['ant', 'bat']
  },
  {
    owner: 'bill',
    pets: ['bat', 'cat']
  },
  {
    owner: 'cody',
    pets: ['cat', 'ant']
  }
];

But what I really want, is an array of pets, and which people have them, like this:

pets = [
  {
    pet: 'ant',
    owners: ['anne', 'cody']
  },
  {
    pet: 'bat',
    owners: ['anne', 'bill']
  },
  {
    pet: 'cat',
    owners: ['bill', 'cody']
  }
];

Is there some tool where I can say, "Transform my input array into an array of unique pet objects, where each output object has a property whose value is an array of owners?"

Or do I need to write this by hand?

Answer 1

You could build a new array with the help of a hash table and iterate all owners and all pets.

var owners = [{ owner: 'anne', pets: ['ant', 'bat'] }, { owner: 'bill', pets: ['bat', 'cat'] }, { owner: 'cody', pets: ['cat', 'ant'] }],
    pets = [];

owners.forEach(function (owner) {
    owner.pets.forEach(function (pet) {
        if (!this[pet]) {
            this[pet] = { pet: pet, owners: [] }
            pets.push(this[pet]);
        }
        this[pet].owners.push(owner.owner);
    }, this)
}, Object.create(null));

console.log(pets);

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