Optimise nested for loop and if statement in javascript

Question

I have an if statement inside two nested for loops in my javascript code as below.

The problem is that the execution slows down when I have to compare thousands of objects in the array as the loop iterates through the entire array just to check for a single matching value.

When the key in data object matches with the id of an object from the arr array it adds a username key to the objects in arr array.

Please run the following code and see the output :

var data = { 1: 'John',
  2: 'Josehp',
  8: 'Marley',
  3: 'George',
  4: 'Stella',
  5: 'Stanley',
  123: 'Juhi'
}



var arr = [ { id: '1'
   },
  { id: '2'
  },
  { id: '10'
    },
  { id: '3'
    },
  { id: '4'
    },
  { id: '13'
    },
  { id: '5'
    }
];

var x;
for (x in data) {
	for (i = 0; i < arr.length; i++) {
	if (arr[i].id == x) {
	arr[i].username = data[x];
	}
     }
  }
console.log(arr)

How can I optimise this code to avoid nested loops or simply improve the performance ?

if loop? Do you mean if statement?

nick zoum
– nick zoum

2019-04-02 07:13:16 +00:00
Commented Apr 2, 2019 at 7:13 — nick zoum
– nick zoum, Commented Apr 2, 2019 at 7:13
corrected it. thank you

node_man
– node_man

2019-04-02 07:13:59 +00:00
Commented Apr 2, 2019 at 7:13 — node_man
– node_man, Commented Apr 2, 2019 at 7:13

Alexey Semerenko · Accepted Answer · 2019-04-02 07:20:47Z

1

may be something like this will help?

arr.forEach((user) => {
    if (data[user.id] !== undefined) {
        user.username = data[user.id]
    }
});

answered Apr 2, 2019 at 7:20

Alexey Semerenko

1321 silver badge6 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

node_man Over a year ago

really loved this short answer

Nina Scholz · Accepted Answer · 2019-04-02 07:13:11Z

1

You could take a single loop and check if the object exists and update the array.

var data = { 1: 'John', 2: 'Josehp', 8: 'Marley', 3: 'George', 4: 'Stella', 5: 'Stanley', 123: 'Juhi' },
    array = [ { id: '1' }, { id: '2' }, { id: '10' }, { id: '3' }, { id: '4' }, { id: '13' }, { id: '5' }],
    i;

for (i = 0; i < array.length; i++) {
    if (array[i].id in data) {
        array[i].username = data[array[i].id];
    }
}

console.log(array);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Apr 2, 2019 at 7:13

Nina Scholz

388k26 gold badges367 silver badges417 bronze badges

Comments

0xc14m1z · Accepted Answer · 2019-04-02 07:15:57Z

1

data is an hash with id as key, so access it's elements by id is an O(1) operation.

This means that you can have a single loop through your arr variable making your algorithm linear (O(n)):

for (let i = 0; i < arr.length; i++ )
  if ( data[arr[i].id] )
    arr[i].username = data[arr[i].id]

answered Apr 2, 2019 at 7:15

0xc14m1z

3,7252 gold badges16 silver badges24 bronze badges

Comments

arizafar · Accepted Answer · 2019-04-02 07:16:18Z

1

You can use Array.prototype.map and ternary.

var data = { 1: 'John',
  2: 'Josehp',
  8: 'Marley',
  3: 'George',
  4: 'Stella',
  5: 'Stanley',
  123: 'Juhi'
}



var arr = [ { id: '1'
   },
  { id: '2'
  },
  { id: '10'
    },
  { id: '3'
    },
  { id: '4'
    },
  { id: '13'
    },
  { id: '5'
    }
];

let out = arr.map(({id}) => (data[id]? {id, username: data[id]}: {id}));
console.log(out)

answered Apr 2, 2019 at 7:16

arizafar

3,1321 gold badge11 silver badges19 bronze badges

Comments

Jack Bashford · Accepted Answer · 2019-04-02 07:20:08Z

1

Just use map with a ternary operator and spreading:

var data = { 1: 'John', 2: 'Josehp', 8: 'Marley', 3: 'George', 4: 'Stella', 5: 'Stanley', 123: 'Juhi'}

var arr = [{id: '1'},{id: '2'},{id: '10'},{id: '3'},{id: '4'},{id: '13'},{id: '5'}];

arr = arr.map(e => data[e.id] ? { ...e, username: data[e.id] } : e);

console.log(arr)

.as-console-wrapper { max-height: 100% !important; top: auto; }

answered Apr 2, 2019 at 7:20

Jack Bashford

44.3k11 gold badges56 silver badges84 bronze badges

Comments

nick zoum · Accepted Answer · 2019-04-02 07:22:50Z

1

You could just loop through the arr array and set each item's username based on the property of data with the same key.

var data = {
  1: 'John',
  2: 'Josehp',
  8: 'Marley',
  3: 'George',
  4: 'Stella',
  5: 'Stanley',
  123: 'Juhi'
};

var arr = [{ id: '1' },
{ id: '2' },
{ id: '10' },
{ id: '3' },
{ id: '4' },
{ id: '13' },
{ id: '5' }];


arr.forEach(function(item) {
  item.username = data[item.id];
});
console.log(arr);

edited Apr 2, 2019 at 7:22

answered Apr 2, 2019 at 7:15

nick zoum

6,6538 gold badges43 silver badges93 bronze badges

Comments

Diptyajit Mitra · Accepted Answer · 2019-04-02 07:28:39Z

1

var data = { 1: 'John', 2: 'Josehp', 8: 'Marley', 3: 'George', 4: 'Stella', 5: 'Stanley', 123: 'Juhi' },
array = [ { id: '1' }, { id: '2' }, { id: '10' }, { id: '3' }, { id: '4' }, { id: '13' }, { id: '5' }],
i;

for (var m in array){
 array[m].username = data[array[m].id]
}

console.log(array);

answered Apr 2, 2019 at 7:28

Diptyajit Mitra

1442 bronze badges

Collectives™ on Stack Overflow

Optimise nested for loop and if statement in javascript

7 Answers 7

1 Comment

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

7 Answers 7

1 Comment

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related