How to isolate duplicates by property from an array of objects

Question

From this array of objects, I'd like to get multiple arrays containing the objects that have the same values for the "id" property:

var obj1 = { id: 1, name: "apple"};
var obj2 = { id: 2, name: "pear"};
var obj3 = { id: 3, name: "melon"};
var obj4 = { id: 4, name: "cherry"};
var obj5 = { id: 2, name: "banana"};
var obj6 = { id: 1, name: "pinapple"};
var obj7 = { id: 1, name: "peach"};
var array = [obj1, obj2, obj3, obj4, obj5, obj6, obj7];

Example of the arrays I'd like to retrieve:

[{
  id: 1,
  name: "apple"
}, {
  id: 1,
  name: "pinapple"
}, {
  id: 1,
  name: "peach"
}]

[{
  id: 2,
  name: "pear"
}, {
  id: 2,
  name: "banana"
}]

something similar i had stackoverflow.com/questions/71455033/… — cmgchess
– cmgchess, Commented Mar 15, 2022 at 18:00

Koba · Accepted Answer · 2022-03-17 06:46:30Z

3

There's a groupBy utility function in a library like lodash that you can use, otherwise you'd have to write your own version of that. It would look something like

function myGroupById (array) {
    const group = {};

    array.forEach(elem => {
        group[elem.id] = group[elem.id] || [];
        group[elem.id].push(elem)
    })

    return group;
}

function extractDuplicatesOnly(array) {
    for (const obj in array) {
        if (array[obj].length < 2) {
            delete array[obj]; 
        }
    }
    return array;
}
myArray = myGroupById(myArray);
myArray = extractDuplicatesOnly(myArray);
console.log(myArray);

applying that to your data will yield an object that looks like this:

{
  1: [
    { id: 1, name: "apple" },
    { id: 1, name: "pinapple" },
    { id: 1, name: "peach" },
  ],
  2: [
    { id: 2, name: "pear" },
    { id: 2, name: "banana" },
  ]
};

edited Mar 17, 2022 at 6:46

Koba

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answered Mar 15, 2022 at 18:01

Joshua Wood

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1 Comment

Koba Over a year ago

Thank you very much Joshua. I made some edits to your answer to match my question.

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