Filtering an array of objects that contain arrays

Question

This is a smaller version of the array i have but it has the same structure

with const arr below, i want to create 2 new arrays with unique values that are sorted in ascending order

const arr = [{
    tags: ['f', 'b', 'd'],
    weight: 7,
    something: 'sdfsdf'
  },
  {
    tags: ['a', 'b', 'c', 'd', 'e'],
    weight: 6,
    something: 'frddd'
  },
  {
    tags: ['f', 'c', 'e', 'a'],
    weight: 7,
    something: 'ththh'
  },
  {
    tags: ['a', 'c', 'g', 'e'],
    weight: 5,
    something: 'ghjghj'
  }
];

const finalTags = [];
const finalWeight = [];

// TODO:  find a better way to do this
arr.forEach(v => {
  if (finalWeight.indexOf(v.weight) === -1) finalWeight.push(v.weight);
  v.tags.forEach(val => {
    if (finalTags.indexOf(val) === -1) finalTags.push(val);
  });
});

// Ascending order
finalTags.sort();
finalWeight.sort();

what i have above works, but seems a bit messy and was wandering if there was a better/tidier way of doing this

Answer 1

You can use Array.prototype.reduce() combined with Set in order to get an object with the sorted arrays {tags: [], weights: []}:

const arr = [{tags: ['f', 'b', 'd'],weight: 7,something: 'sdfsdf'},{tags: ['a', 'b', 'c', 'd', 'e'],weight: 6,something: 'frddd'},{tags: ['f', 'c', 'e', 'a'],weight: 7,something: 'ththh'},{tags: ['a', 'c', 'g', 'e'],weight: 5,something: 'ghjghj'}];
const obj = arr.reduce((a, {tags, weight}) => {
  a.tags = [...new Set(a.tags.concat(tags))];
  a.weights = [...new Set(a.weights.concat(weight))];
  return a;
}, {tags: [], weights: []});

// final result i want
console.log('finalTags:', obj.tags.sort()); // ['a', 'b', 'c', 'd', 'e', 'f', 'g'];
console.log('finalWeight:', obj.weights.sort()); // [5, 6, 7];

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