Remove original and duplicate from an array of objects - JS

Question

I have an array of objects.

const arr = [
  { title: \"sky\", artist: \"Jon\", id: 1 },
  { title: \"rain\", artist: \"Paul\", id: 2 },
  { title: \"sky\", artis         


        

Answer 1

You could run the array through reduce() and then use some to see if you should add if it does not exist, or remove using filter if it does.

Snippet:

const arr = [
  { title: "sky", artist: "Jon", id: 1  },
  { title: "rain", artist: "Paul", id: 2  },
  { title: "sky", artist: "Jon", id: 1  },
  { title: "rain", artist: "Paul", id: 2  },
  { title: "earth", artist: "Frank", id: 3  },
];

const unique = arr.reduce((accumulator, currentValue) => { 
  // add if we don't have
  if (!accumulator.some(x => x.id === currentValue.id)) {
    accumulator.push(currentValue);
  } else {
    // remove if we do
    accumulator = accumulator.filter(x => x.id !== currentValue.id);
  }
  
  return accumulator;
}, []); 

console.info(unique);

Answer 2

you can do it in one line like this:

const res = arr.filter(elem => (arr.filter(obj => obj.id === elem.id)).length === 1)

or you can do it like this(better in terms of time complexity):

const arr = [
  { title: "sky", artist: "Jon", id: 1  },
  { title: "rain", artist: "Paul", id: 2  },
  { title: "sky", artist: "Jon", id: 1  },

];

const counts = arr.reduce((counts, curr) => (counts[curr.id] = ++counts[curr.id] || 1, counts), {})
const res = arr.filter(curr => counts[curr.id] === 1)

Answer 3

If you know the title, artist, id are gonna be in the same order in each of the object, one solution can be this:

var arrayX=[
  { title: "sky", artist: "Jon", id: 1 },
  { title: "rain", artist: "Paul", id: 2 },
  { title: "sky", artist: "Jon", id: 1 }
];
var newArray = arrayX.map(i=> JSON.stringify(i)); //stringify all the objects so as to compare them
var res = newArray.filter((elem, index)=>{
  if(newArray.indexOf(elem) === newArray.lastIndexOf(elem)){
    return elem //get only those elements whihc do not have dupes
  }
}); 
var finalResult = res.map(i=>JSON.parse(i)); //parse the result to get the array of object
console.log(finalResult)

Answer 4

That's a one-liner:

list.filter(el => list.filter(e => e.title == el.title).length == 1);

const arr = [{
    title: "sky",
    artist: "Jon",
    id: 1
  },
  {
    title: "rain",
    artist: "Paul",
    id: 2
  },
  {
    title: "sky",
    artist: "Jon",
    id: 1
  }
];

const arr1 = [{
    title: "sky",
    artist: "Jon",
    id: 1
  },
  {
    title: "rain",
    artist: "Paul",
    id: 2
  },
  {
    title: "sky",
    artist: "Jon",
    id: 1
  },
  {
    title: "rain",
    artist: "Paul",
    id: 2
  }
];


function removeDupes(list) {
  return list.filter(el => list.filter(e => e.id == el.id).length == 1);
}

console.log(removeDupes(arr));
console.log(removeDupes(arr1));

Answer 5

You could take an object and filter with the value of the hash table.

const
    array = [{ title: "sky", artist: "Jon", id: 1 }, { title: "rain", artist: "Paul", id: 2 }, { title: "sky", artist: "Jon", id: 1 }, { title: "rain", artist: "Paul", id: 2 }],
    ids = array.reduce((r, { id }) => (r[id] = !(id in r), r), {}),
    result = array.filter(({ id }) => ids[id]);

console.log(result);

Answer 6

You can group the items by id, and then use _.flatMap() to convert back a single array. In the _.flatMap() callback return an empty array if the group has more than one item:

const fn = arr => _.flatMap(
  _.groupBy(arr, 'id'), // group by the id
  group => _.size(group) > 1 ? [] : group // check the size and return an empty array for groups with more than a single item
)

const arr1 = [{"title":"sky","artist":"Jon","id":1},{"title":"rain","artist":"Paul","id":2},{"title":"sky","artist":"Jon","id":1}]
const arr2 = [{"title":"sky","artist":"Jon","id":1},{"title":"rain","artist":"Paul","id":2},{"title":"sky","artist":"Jon","id":1},{"title":"rain","artist":"Paul","id":2}]

console.log(fn(arr1))
console.log(fn(arr2))

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