Copy single field of all objects in array in single array

Question

I wanted to optimize my code removing a for-loop.

    groupFieldNames = [];
    for (i = 0; i < data.length; i++) {
        groupFieldNames.push(data[i].groupFieldName);
    }

data is an array of objects, each having 4 fields.

I am interested in the one identified as groupFieldName.

Is there a way to avoid the loop and directly push the fields in the array?

EDIT:

I went with @Yosvel Quintero suggestion (to all the guys suggesting the map solution, he was the first one), and checked the performance. With a data array having ~60k objects I've got:

3ms using map;
11ms using for-loop

Not bad.

You can use .map instead, but if you're looking for optimal efficient code, not much can beat a for loop... — CertainPerformance
– CertainPerformance, Commented Feb 27, 2019 at 9:52
You can use map, or forEach, whatever, it will iterate, just the loop won't be in your code, but you cannot avoid it. — sjahan
– sjahan, Commented Feb 27, 2019 at 9:53
Don't know your requirement but maybe you can keep the complete object and wherever you need groupFieldName, simply use object destructure {groupFieldName} = obj; or in methods methodName({groupFieldName}){//} — arizafar
– arizafar, Commented Feb 27, 2019 at 10:03

Yosvel Quintero · Accepted Answer · 2019-02-27 09:53:39Z

2

You can use Array.prototype.map()

const groupFieldNames = [];
for (i = 0; i < data.length; i++) {
    groupFieldNames.push(data[i].groupFieldName);
}

To:

const groupFieldNames = data.map(o => o.groupFieldName);

answered Feb 27, 2019 at 9:53

Yosvel Quintero

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1 Comment

Oiproks Over a year ago

As @sjahan pointed out, this still counts a loop, even if you cannot see it. I was looking for something like mem-copy or stuff like that. But i see the elegance in what you proposed.

Tushar Walzade · Accepted Answer · 2019-02-27 09:55:22Z

1

You could effectively use Array's built-in .map() here as follows -

var data = [
	{ id: 1, groupFieldName: 'abcd' },
	{ id: 2, groupFieldName: 'pars' }
];
var groupFieldNames = data.map(obj => obj.groupFieldName)
console.log(groupFieldNames);

answered Feb 27, 2019 at 9:55

Tushar Walzade

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Comments

ellipsis · Accepted Answer · 2019-02-27 10:01:26Z

1

You can use map

var groupFieldNames = [];
var data=[{groupFieldName:'a'},{groupFieldName:'b'},{groupFieldName:'c'}]
  console.log(data.map(x=>x.groupFieldName))

You can also use forEach

var groupFieldNames = [];
var data=[{groupFieldName:'a'},{groupFieldName:'b'},{groupFieldName:'c'}]
data.forEach(x=>groupFieldNames.push(x.groupFieldName))
  console.log(groupFieldNames)

edited Feb 27, 2019 at 10:01

answered Feb 27, 2019 at 9:56

ellipsis

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Comments

Mamun · Accepted Answer · 2019-02-27 10:15:15Z

1

You can use Array.prototype.map() with Destructuring assignment in the following way:

const data = [
  {id: 66, groupFieldName: 'test', other: 'other'},
  {id: 66, groupFieldName: 'test2', other: 'other2'}
];

const groupFieldNames = data.map(({groupFieldName}) => groupFieldName);
console.log(groupFieldNames);

edited Feb 27, 2019 at 10:15

answered Feb 27, 2019 at 10:06

Mamun

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