Create new object from existing array and object

Question

I'm trying to return a new object with properties given in the existing object and keys present in a given array. I can't mutate the object and if the keys are present in the array but not in the object the key should be ignored. I get hung up on how to compare the array elements to the objects keys.

function picker(array, obj) {
    var newObj = {};
    for (var i = 0; i < arrary.length; i++) {
        if (array[i] !== obj[i]) {
            newObj[array[i]] = obj[i];
        }
    }
    return newObj;
}

var array = [
    'a',
    'c',
    'e'
];
var obj = {
    a: 1,
    b: 2,
    c: 3,
    d: 4
};

var bubble = picker(array, obj);
console.log(bubble);   result --> `{ a: 1, c: 3 }`

Oriol · Accepted Answer · 2016-11-21 23:08:13Z

2

You probably meant something like this:

function picker(array, obj) {
  var newObj = {};
  for (var i = 0; i < array.length; i++) {
    if (array[i] in obj) {
      newObj[array[i]] = obj[array[i]];
    }
  }
  return newObj;
}
var array = ['a', 'c', 'e'];
var obj = {a: 1, b: 2, c: 3, d: 4};
console.log(picker(array, obj));

That is, if obj contains the property with name array[i], then add that property to newObj.

Maybe it will be clearer if you iterate with reduce, forEach or for...of, then you won't be confused by the index i.

function picker(array, obj) {
  return array.reduce(function(newObj, key) {
    if (key in obj) newObj[key] = obj[key];
    return newObj;
  }, {});
}
var array = ['a', 'c', 'e'];
var obj = {a: 1, b: 2, c: 3, d: 4};
console.log(picker(array, obj));

answered Nov 21, 2016 at 23:08

Oriol

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Comments

rishat · Accepted Answer · 2016-11-21 23:12:22Z

1

You could do something like

const x = array.reduce((total, current) => current in obj ? ({
  ...total,
  [current]: obj[current]
}) : total, {});

Which basically creates an object, key after key, based only on items of the array, where the value per key is taken from obj. Check out the fiddle.

answered Nov 21, 2016 at 23:12

rishat

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Comments

Aruna · Accepted Answer · 2016-11-21 23:12:20Z

0

You haven't checked whether the key is existing in the array.

The condition if (array[i] !== obj[i]) { is trying to check the array key with object value instead of object key. Also obj[i] is incorrect, since obj[0] does not exist with the key 0.

This is another variation using Object.keys instead of for loop.

function picker(array, obj) {
  var newObj = {};
  Object.keys(obj).forEach(function(key){
    if(array.indexOf(key) > -1) {
      newObj[key] = obj[key];
    }
  });
  
  return newObj;
}
var array = ['a', 'c', 'e'];
var obj = {a: 1, b: 2, c: 3, d: 4};
console.log(picker(array, obj));

answered Nov 21, 2016 at 23:12

Aruna

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