Sum up array with objects

Question

I am having the following array with objects and I would like to sum up all occurrences of watt:

let allProducts = [{
    "unique_id": "102",
    "currency": "$",
    "price": "529.99",
    "watt": 150
  },
  {
    "unique_id": "11",
    "currency": "$",
    "price": "323",
    "watt": 150
  },
  {
    "unique_id": "13",
    "currency": "$",
    "price": "23",
    "watt": 77
  }
]

let getWatt =
  _(allProducts)
  .map((objs, key) => ({
    'watt': _.sumBy(objs, 'watt')
  }))
  .value()

console.log(getWatt)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

As you can see I get back an array of 0 values. However, I would like to get back the result value of 377. Any suggestions what I am doing wrong?

I appreciate your replies!

baao · Accepted Answer · 2018-06-03 19:30:25Z

15

It's easy using plain js

const sum = allProducts.reduce((a, {watt}) => a + watt, 0);
console.log(sum);

<script>
let allProducts = [{
    "unique_id": "102",
    "currency": "$",
    "price": "529.99",
    "watt": 150
  },
  {
    "unique_id": "11",
    "currency": "$",
    "price": "323",
    "watt": 150
  },
  {
    "unique_id": "13",
    "currency": "$",
    "price": "23",
    "watt": 77
  }
]


</script>

answered Jun 3, 2018 at 19:30

baao

73.5k18 gold badges151 silver badges208 bronze badges

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Comments

Muhammad Usman · Accepted Answer · 2018-06-03 19:37:03Z

I've read the answers, but I'd like to add an explanation to your problem. The reason you're getting an array is because of using .map. As map returns you the array not a single element. Moreover, you are expecting to get the returned array as modified and map doesn't do that.

What you're trying to achieve is can be done using .reduce. I mean that's why .reduce is there

let allProducts = [{
    "unique_id": "102",
    "currency": "$",
    "price": "529.99",
    "watt": 150
  },
  {
    "unique_id": "11",
    "currency": "$",
    "price": "323",
    "watt": 150
  },
  {
    "unique_id": "13",
    "currency": "$",
    "price": "23",
    "watt": 77
  }
];
var getWatt = allProducts.reduce((acc,curr)=> acc + curr.watt,0);
console.log(getWatt);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

amrender singh · Accepted Answer · 2018-06-03 19:31:40Z

1

Try the following:

let allProducts = [{
    "unique_id": "102",
    "currency": "$",
    "price": "529.99",
    "watt": 150
  },
  {
    "unique_id": "11",
    "currency": "$",
    "price": "323",
    "watt": 150
  },
  {
    "unique_id": "13",
    "currency": "$",
    "price": "23",
    "watt": 77
  }
];

var sum = allProducts.reduce((sum,a)=>{
  return sum + a.watt;
},0);
console.log(sum);

answered Jun 3, 2018 at 19:31

amrender singh

8,2594 gold badges27 silver badges30 bronze badges

Comments

Nina Scholz · Accepted Answer · 2018-06-03 19:50:18Z

Just take a single _.sumBy with the array of objects and the wanted key watt for summing.

Your attempt uses an object, instead of an array for _.sumBy. The object is not an array and the return value is zero.

var allProducts = [{ unique_id: "102", currency: "$", price: "529.99", watt: 150 }, { unique_id: "11", currency: "$", price: "323", watt: 150 }, { unique_id: "13", currency: "$", price: "23", watt: 77 }],
    getWatt = _.sumBy(allProducts, 'watt');

console.log(getWatt)

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.10/lodash.min.js"></script>

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