Convert object to array while removing non-number field names

Question

Is it possible to convert an object to an array if it has this structure, while all fields are ignored which have an non-number field?

var obj = {
    0: 'some',
    1: 'thing',
    2: 'to convert',
    ignore: 'this'
}

result should be:

result = ['some', 'thing', 'to convert'];

with the correct order of the elements.

Note being numerical is not enough to be an array index. `""`, `"-0"`, `" 0"`, `"1.2"`, `"4294967295"`, `"Infinity"` are not array indices. — Oriol, Jul 02 '16 at 18:19

score 4 · Accepted Answer · edited May 23 '17 at 12:22

If it has a length property, you can use Array.from:

console.log(Array.from({
  0: 'some',
  1: 'thing',
  2: 'to convert',
  length: 3,
  ignore: 'this'
}));

Otherwise, assuming the indices are not sparse, you can iterate manually. Start from 0 and increment until you reach the end.

var obj = {
  0: 'some',
  1: 'thing',
  2: 'to convert',
  ignore: 'this'
}, array = [], i = -1;
while(++i in obj) array[i] = obj[i];
console.log(array);

In general, you would need to iterate all string properties and check if they are array indices:

function isArrayIndex(str) {
  return (str >>> 0) + '' === str && str < 4294967295
}
var obj = {
  0: 'some',
  1: 'thing',
  2: 'to convert',
  ignore: 'this'
}, array = [];
for(var key of Object.keys(obj))
  if(isArrayIndex(key)) array[key] = obj[key];
console.log(array);

score 0 · Answer 2 · answered Jul 02 '16 at 17:49

0

A faster but more complex way is :

var obj = {
  0: 'some',
  1: 'thing',
  2: 'to convert',
  ignore: 'this'
}, res = [], keys = Object.getOwnPropertyNames(obj);

for(var i = 0; i < keys.length; i++)
  if(!isNaN(+keys[i]))
    res.push(obj[keys[i]]);

answered Jul 02 '16 at 17:49

ClementNerma

1,079
1
11
16

1

`isNaN` is not the proper way to check array indices. – Oriol Jul 02 '16 at 18:00
This function is here to check if the array is a number of not – ClementNerma Jul 02 '16 at 18:26

Jose Hermosilla Rodrigo · Answer 3 · 2016-07-02T18:40:13.120

-1

You can do something like this:

var obj = {
    0: 'some',
    1: 'thing',
    2: 'to convert',
    ignore: 'this'
};

var copy = {};

Object.keys(obj).forEach(e=>{
  if(!isNaN(e)) copy[e] = obj[e];
});

console.log(Object.values(copy));

edited Jul 02 '16 at 18:40

answered Jul 02 '16 at 18:01

Jose Hermosilla Rodrigo

3,513
6
22
38

The downvoter (not me) might have thought that instead of copying all properties and deleting non-numeric ones, it would be better to copy only the desired ones. – Oriol Jul 02 '16 at 18:26
@Oriol Thank you for the input! fixed now! – Jose Hermosilla Rodrigo Jul 02 '16 at 18:41
Your code has a little problem : it's not ES5-compatible, only ES6 which is not implemented in all browsers. – ClementNerma Jul 02 '16 at 21:29

Convert object to array while removing non-number field names

3 Answers3