How to double the numbers in an array of objects?

Question

I want to double the key values in an array of objects and I always end up getting the last key:val in the list. I want to be able to print the whole array of objects doubled their values.

doubleArr = [];

function doubleSize (a,b) {
    for(var i in a) {
        if (a.hasOwnProperty(i)) {
            var doubleObj = {};
            doubleObj[i] = b * a[i];
            var results = doubleObj[i];
            doubleArr.push(results);

        }

    }

    return doubleObj;
}

console.log(doubleSize({1:1,1:2,1:3,1:4,1:5}, 2))

I only get {1:10}. The goal is to get {1:2,1:4,1:6,1:8,1:10}. Thanks.

Your object has only one property, `1`. Duplicate properties overwrite earlier values. Before the object is even passed to the function, it is evaluated to `{ 1: 5 }`. — CertainPerformance, Aug 28 '18 at 01:10
@Lee Taylor But still it's not giving me the results I wanted. DoubleArr returns [10]. The goal is to return the array of objects. — Michael Stokes, Aug 28 '18 at 01:10
You're using the same key for each object `1`...As @CertainPerformance states, so you only have one object passed to your function. — Lee Taylor, Aug 28 '18 at 01:12
To be more precise, he has only one *key-value* pair in the passed object. — CertainPerformance, Aug 28 '18 at 01:14
@LeeTaylor so you're saying using the same key is the problem? I should change them to different keys? I tried that and I still end of getting the last key:val pair. — Michael Stokes, Aug 28 '18 at 01:15
type `console.log({1:1,1:2,1:3,1:4,1:5})` to see the problem in glorious detail — Jaromanda X, Aug 28 '18 at 01:18
Because 1 is being used as the same ID/key throughout. They have to be unique! — Lee Taylor, Aug 28 '18 at 01:22
This question didn't deserved to be downvoted. I'm still learning. Thanks. — Michael Stokes, Aug 28 '18 at 01:33

Lee Taylor · Answer 1 · 2018-08-28T01:19:16.997

0

You are using the same key for your objects 1. I am assuming that you don't need objects as they don't provide anything obvious to your code:

Edit If you insist on using objects, I have provided the second version also.

function doubleSize (a,b) 
{
    var doubleArr = [];
    for(var i=0; i<a.length;i++) 
    {
        doubleArr.push(a[i]*b);
    }

    return doubleArr;
}

console.log(doubleSize([1,2,3,4,5], 2))

function doubleSize2 (a,b) 
{
    var result = {};
    for(var i in a)
    {
        result[i] = a[i]*b
    }

    return result;
}

console.log(doubleSize2({a:1,b:2,c:3,d:4,e:5}, 2))

edited Aug 28 '18 at 01:19

answered Aug 28 '18 at 01:16

Lee Taylor

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Yes it does work when I change the keys and return as doubleArr, I get the array of numbers doubled. – Michael Stokes Aug 28 '18 at 01:17
1

`const doubleSize = (a, b) => a.map(n => n * b)` works too :p – Jaromanda X Aug 28 '18 at 01:18

score 0 · Accepted Answer · answered Aug 28 '18 at 01:18

The primary issue with your code is that you cannot have duplicate keys in an object. Every key in an object must be unique; otherwise, you are essentially redeclaring the value associated with that key over and over (so, naturally, in your example, the key 1 will end up being associated with the last value you assign it: 5).

However, even if you used an object without duplicate keys, you still have the following issues:

Your doubleArr should not be declared in the global scope, but instead within the function; moreover, you don't need an array for what you're doing
Your code is actually constructing an array of objects rather than an object. If you want to return an object, you should build up an object with unique values in your function.

Here's an example of a modified version of your code:

function doubleSize (a,b) {
    var doubleObj = {};
    for(var i in a) {
        if (a.hasOwnProperty(i)) {
            doubleObj[i] = b * a[i];
        }
    }

    return doubleObj;
}

console.log(doubleSize({1:1,2:2,3:3,4:4,5:5}, 2)) // Note the unique keys

However, I don't fully understand the need for objects. You could use arrays instead, and then replace all of your code with a simple one-liner using Array.map:

var arr = [1, 2, 3, 4, 5]
var doubledArr = arr.map(x => 2*x) // An arrow function that multiplies each value in the array by 2
console.log(doubledArr)

That's what I've been looking for. I see where I went wrong. Still got lots to learn about objects. Thanks. — Michael Stokes, Aug 28 '18 at 01:25
I can do the same with arrays, but I want to be able to them with objects as well. — Michael Stokes, Aug 28 '18 at 01:26

score 0 · Answer 3 · answered Aug 28 '18 at 01:26

You can't have duplicate keys in an object, you can have an array of objects with the same key though. Something like:

function doubleSize (a, b) {
  var out = [];
  for(var i = 0; i < a.length; i++) {
    out.push({'1': a[i]['1'] * b});
  }

  return out;
}

console.log(doubleSize([{'1': 1}, {'1': 2}, {'1': 3}, {'1': 4}, {'1': 5}], 2));

score 0 · Answer 4 · answered Aug 28 '18 at 01:51

0

function doubleSize (a,b) {
    var midObject = {};
    for(var i in a) {
        if (a.hasOwnProperty(i)) {
            midObject[i] = b * a[i];
        }
    }

    return midObject;
}

console.log(doubleSize({1:1,2:2,3:3,4:4,5:5}, 5))

answered Aug 28 '18 at 01:51

James Cameron

1

How to double the numbers in an array of objects?

4 Answers4