Removing Duplicates in Array of Objects based on Property Values

Question

I have an array of objects I am trying to find duplicates based on some properties (first and last). My logic appears to be off and here is what I have tried.

My final result should look similar to:

[
  {first:"John", last: "Smith", id:"1234", dupes: [555,666]},
  {first:"John", last: "Jones", id:"333", dupes: []}
];

let arrayOfObjects = 
[
  {first:"John", last: "Smith", id:"1234", dupes: []},
  {first:"John", last: "Smith", id:"555", dupes: []},
  {first:"John", last: "Jones", id:"333", dupes: []},
  {first:"John", last: "Smith", id:"666", dupes: []}
];


arrayOfObjects.forEach(record => {
  arrayOfObjects.forEach(rec => {
  if(record.first == rec.first &&
      record.last == rec.last &&
      record.id !== rec.id){
        console.log("match found for: " + JSON.stringify(record) + " and: " + JSON.stringify(rec));
        
        record.dupes.push(rec.id);
        //probably need to remove something here
      }
  });
});

console.log(JSON.stringify(arrayOfObjects));

Please don't use `.map` for simple iteration. Use it when you want to transform the array into another array. If you need to just go through the values, then use `.forEach()` or a normal loop. — VLAZ, Mar 18 '20 at 14:45
You should find inspiration from [How to find duplicate values in a JavaScript array of objects, and output only unique values?](https://stackoverflow.com/q/39885893/215552) — Heretic Monkey, Mar 18 '20 at 14:46

score 1 · Accepted Answer · answered Mar 18 '20 at 14:57

First off, please don't use .map() when not performing a mapping operation. I've substituted the usage of .map with .forEach as the latter is more appropriate in this case.

Second, your comment //probably need to remove something here is correct - you do have to remove an item. Namely, you have to remove the duplicate item rec that was just found. To do that, you can utilise Array#splice which requires the index to be removed. You can easily get the index as the second parameter of the .forEach() callback

let arrayOfObjects = 
[
  {first:"John", last: "Smith", id:"1234", dupes: []},
  {first:"John", last: "Smith", id:"555", dupes: []},
  {first:"John", last: "Jones", id:"333", dupes: []},
  {first:"John", last: "Smith", id:"666", dupes: []}
];


arrayOfObjects.forEach(record => {
  arrayOfObjects.forEach((rec, index) => {
// get index ------------------^^^^^-->------------------>--------------v
  if(record.first == rec.first &&       //                              |
      record.last == rec.last &&        //                              |
      record.id !== rec.id){            //                              |
        record.dupes.push(rec.id);      //                              |
        arrayOfObjects.splice(index, 1) //<--- remove using the index --<
      }
  });
});

console.log(JSON.stringify(arrayOfObjects));

Removing Duplicates in Array of Objects based on Property Values

1 Answers1