Finding Duplicates in array of object in javascipt by map method-CodePudding

I am trying to remove duplicate from an array of object in Javascript. Below is the code which doesnot work, it is creating Array of map of size 4.

let arr = [{id: 32, name: 'Name1', age: 88},
  {id: 33, name: 'Name2', age: 88},
  {id: 32, name: 'Name3', age: 88},
  {id: 1, name: 'Sam', age: 88},
  {id: 33, name: 'Name2', age: 88},
  {id: 2, name: 'Tom', age: 88}
];

console.log(arr)

let mp1 = new Map();
let uniqueElements = arr.map( obj => mp1.set(obj.id, obj))

console.log(uniqueElements);

CodePudding user response：

map returns the new array with the same length of the calling array

For accumulated value (here is mp1), you should use reduce

let uniqueElements = arr.reduce(
  (mp1, obj) => mp1.set(obj.id, obj),
  new Map()
)

let arr = [
  { id: 32, name: 'Name1', age: 88 },
  { id: 33, name: 'Name2', age: 88 },
  { id: 32, name: 'Name3', age: 88 },
  { id: 1, name: 'Sam', age: 88 },
  { id: 33, name: 'Name2', age: 88 },
  { id: 2, name: 'Tom', age: 88 },
]

console.log(arr)
let uniqueElements = arr.reduce((mp1, obj) => mp1.set(obj.id, obj), new Map())
console.log(uniqueElements)

CodePudding user response：

Below snippet may be one possible implementation to achieve the desired objective:

const discardDupeIdElements = arr => (
  Object.values(
    arr.reduce(
      (fin, itm) => ({
        ...fin,
        [itm.id]: itm
      }), {}
    )
  )
);

var origArr = [{
    id: 32,
    name: 'Name1',
    age: 88
  },
  {
    id: 33,
    name: 'Name2',
    age: 88
  },
  {
    id: 32,
    name: 'Name3',
    age: 88
  },
  {
    id: 1,
    name: 'Sam',
    age: 88
  },
  {
    id: 33,
    name: 'Name2',
    age: 88
  },
  {
    id: 2,
    name: 'Tom',
    age: 88
  }
];

console.log(discardDupeIdElements(origArr));

Note

This will always keep the last element of a set of duplicates and ignore all earlier ones. Such as for id 32, it will keep the element with name = Name3 and discard Name2.

Fixing the OP's code:

const arr = [{id: 32, name: 'Name1', age: 88},
  {id: 33, name: 'Name2', age: 88},
  {id: 32, name: 'Name3', age: 88},
  {id: 1, name: 'Sam', age: 88},
  {id: 33, name: 'Name2', age: 88},
  {id: 2, name: 'Tom', age: 88}
];

// console.log(arr);
// commented-out for easier viewing of the output

const mp1 = new Map();      // declared a map

arr.forEach(obj => mp1.set(obj.id, obj));
// used .forEach to iterate through the array
// and update the map

const uniqueElements = [...mp1.values()];
// used spread operator to extract 
// the values of the map into an array

console.log(uniqueElements);
// console.log the unique elements

Note

Where possible, used const rather than let.