Compare two arrays of objects and remove items in the second one that have the same property value

Question

All I need to do is compare two arrays of objects and remove items in the second one that have the same property value. For example:

var a = [{'name':'bob', 'age':22}, {'name':'alice', 'age':12}, {'name':'mike', 'age':13}];
var b = [{'name':'bob', 'age':62}, {'name':'kevin', 'age':32}, {'name':'alice', 'age':32}];

function remove_duplicates(a, b) {
    for (var i = 0, len = a.length; i < len; i++) {
        for (var j = 0, len = b.length; j < len; j++) {
            if (a[i].name == b[j].name) {
                b.splice(j, 1);
            }
        }
    }

    console.log(a);
    console.log(b);

}

console.log(a);
console.log(b);

remove_duplicates(a,b);

I cannot understand why this does not work and instead gives:

Uncaught TypeError: Cannot read property 'name' of undefined

What I expected was the following content in b:

[{'name':'kevin', 'age':32}];

Maybe because of redefinition of `len` variable in your loops — frogatto, Jul 24 '13 at 09:46

Snippet · Accepted Answer · 2013-07-25T02:12:43.680

23

FIDDLE

 for (var i = 0, len = a.length; i < len; i++) { 
        for (var j = 0, len2 = b.length; j < len2; j++) { 
            if (a[i].name === b[j].name) {
                b.splice(j, 1);
                len2=b.length;
            }
        }
    }

edited Jul 25 '13 at 02:12

answered Jul 24 '13 at 09:50

Snippet

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Geole · Answer 2 · 2019-04-11T21:36:27.250

6

Instead of using two loops you might also use the findIndex function:

for (var i = 0, len = a.length; i < len; i++) {
    var ItemIndex = b.findIndex(b => b.name === a[i].name);

    a.splice(ItemIndex, 1)
}

Or if you want to go completely without using a loop you might use the forEach function

a.forEach(function(item, index, array) {
    var ItemIndex = b.findIndex(b => b.name === item.name);

    a.splice(ItemIndex, 1)
}

edited Apr 11 '19 at 21:36

answered Apr 11 '19 at 21:10

Geole

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Really loved this type of answer with updated syntax, like writing syntax without old-style for loops. Thank you so much. – Anurag Yadav Nov 16 '20 at 06:28
*without using a loop*: most would count `forEach` as a loop though. – trincot Apr 26 '22 at 08:34

score 4 · Answer 3 · answered Jul 24 '13 at 09:50

Your problem is, that splice() will change the length of the array, so that your precalculated len value will be too large and the inside the loop you try to access undefined elements.

A possible solution would be to use the filter() method:

function remove_duplicates(a, b) {

  b = b.filter( function( item ) {
      for( var i=0, len=a.length; i<len; i++ ){
          if( a[i].name == item.name ) {
              return false;
          }
      }
      return true;
  });

  console.log(a);
  console.log(b);
}

Example Fiddle

Which will also fix the problem of the same `len` in the inner and outer `for` loop. — Andreas, Jul 24 '13 at 09:56

score 3 · Answer 4 · answered Jul 24 '13 at 11:04

3

You just need to break the inner loop when a match is found:

if (a[i].name == b[j].name) {
    b.splice(j, 1);
    break;
}

answered Jul 24 '13 at 11:04

AlwaysALearner

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Dhaval Marthak · Answer 5 · 2013-07-24T09:53:25.587

1

Try this:

You are starting loop from the 0.

for (var i = 0, len = a.length; i < len; i++) {
        for (var j = 0, len = b.length; j < len-1; j++) {
            if (a[i].name == b[j].name) {
                b.splice(j, 1);
            }
        }
    }

Fiddle Demo

edited Jul 24 '13 at 09:53

answered Jul 24 '13 at 09:48

Dhaval Marthak

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score 1 · Answer 6 · answered Oct 02 '14 at 18:39

compare and remove in array of object.Typically array of object data type may be typeOf is object.So that we need to convert into JSON stringify and then check condition..

for(var i=0; i < a.length; i++) {
                    for(var j=0; j < b.length; j++) {
                        if(JSON.stringify(a[i])  == JSON.stringify(b[j])) {
                            a.splice(i, 1);
                        }
                    }
                }

score 1 · Answer 7 · answered Jan 02 '20 at 12:33

let A = [
  {name: 'a', age: 20},
  {name: 'b', age: 30},
  {name: 'c', age: 10},
]

let B = [
  {name: 'a', age: 20},
  {name: 'b', age: 40},
  {name: 'd', age: 10},
  {name: 'e', age: 20},
  {name: 'f', age: 10},
]

const compareName = (obj1, obj2)=>{
  return (obj1.name === obj2.name);
}

const compareAll = (obj1, obj2)=>{
  return (obj1.name === obj2.name && obj1.age=== obj2.age);
}

let output = B.filter(b=>{
  let indexFound = A.findIndex(a => compareName(a, b));
  return indexFound == -1;
})

Depending on which Objects you want to remove use:

compareName : Remove objects which have common name
compareAll : Remove objects which have both name & age common

Also to find common Objects list just add use return index != -1

PS: Refer my Github for Array Data Manipulation examples in Javascript

score 1 · Answer 8 · answered Mar 25 '22 at 11:02

1

var a = [{ 'name': 'bob', 'age': 22 }, { 'name': 'alice', 'age': 12 }, { 'name': 'mike', 'age': 13 }, { 'name': 'keerthi', 'age': 62 }];
var b = [{ 'name': 'bob', 'age': 62 }, { 'name': 'kevin', 'age': 32 }, { 'name': 'alice', 'age': 32 }, { 'name': 'keerthi', 'age': 62 }];

a.map((firstObj) => {
      b.map((compareObj, i) => {
        if (firstObj.name === compareObj.name) {
          b.splice(i, 1);
    }
  })
})

console.log(b)

answered Mar 25 '22 at 11:02

saikeerthi kotha

11
1

Don't use `map` when you don't use its return value. It is a waste of resources to have it create an array. – trincot Apr 26 '22 at 08:31

score 0 · Answer 9 · answered Jul 24 '13 at 09:52

0

The root cause is that you directly splice items from array b while you are in the for loop and pre condition is a and b have same number of items.

answered Jul 24 '13 at 09:52

Phong Vo

1,078
7
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Compare two arrays of objects and remove items in the second one that have the same property value

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