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
– VLAZ, Commented Mar 18, 2020 at 14:45
You should find inspiration from How to find duplicate values in a JavaScript array of objects, and output only unique values? — Heretic Monkey
– Heretic Monkey, Commented Mar 18, 2020 at 14:46

VLAZ · Accepted Answer · 2020-03-18 14:57:16Z

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));

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