How to sum the same objects in array

Question

It is possible to sum the values of an array if they are the same like this:

var COLLECTION = [
  {
    "coords":[1335,2525],
    "items":[
      {id: "boletus",qty: 1},
      {id: "lepiota",qty: 3},
      {id: "boletus",qty: 2},
      {id: "lepiota",qty: 4},
      {id: "carbonite",qty: 4},
    ],
  },
  {
    "coords":[1532,2889],
    "items":[
      {id: "boletus",qty: 2},
      {id: "lepiota",qty: 6},
      {id: "boletus",qty: 1},
      {id: "lepiota",qty: 4},
      {id: "chamomile",qty: 4},
    ],
  }]

To return something like this:

var COLLECTION = [
  {
    "coords":[1335,2525],
    "items":[
      {id: "boletus",qty: 3},
      {id: "lepiota",qty: 7},
      {id: "carbonite",qty: 4},
    ],
  },
  {
    "coords":[1532,2889],
    "items":[
      {id: "boletus",qty: 3},
      {id: "lepiota",qty: 10},
      {id: "chamomile",qty: 4},
    ],
  }]

Wihout losing the other parts of the array? (doing by hand is hard because I have more than 10 thousand duplicates like the example above, and the array have 600 thousand entries.

Nenad Vracar · Accepted Answer · 2018-03-18 19:39:12Z

3

You could use map() to create new array and inside reduce() to group items objects by id and sum qty.

var data = [{"coords":[1335,2525],"items":[{"id":"boletus","qty":1},{"id":"lepiota","qty":3},{"id":"boletus","qty":2},{"id":"lepiota","qty":4},{"id":"carbonite","qty":4}]},{"coords":[1532,2889],"items":[{"id":"boletus","qty":2},{"id":"lepiota","qty":6},{"id":"boletus","qty":1},{"id":"lepiota","qty":4},{"id":"chamomile","qty":4}]}]
  
const result = data.map(function({coords, items}) {
  return {coords, items: Object.values(items.reduce(function(r, e) {
    if(!r[e.id]) r[e.id] = Object.assign({}, e)
    else r[e.id].qty += e.qty
    return r;
  }, {}))}
})  

console.log(result)

edited Mar 18, 2018 at 19:39

answered Mar 18, 2018 at 18:40

Nenad Vracar

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1 Comment

Nina Scholz Over a year ago

your result looks different than expected.

Nina Scholz · Accepted Answer · 2018-03-18 18:56:21Z

You could take the power of Map and render the result by using Array.from with a mapping function which builds new objects for items.

var COLLECTION = [{ coords: [1335, 2525], items: [{ id: "boletus", qty: 1 }, { id: "lepiota", qty: 3 }, { id: "boletus", qty: 2 }, { id: "lepiota", qty: 4 }, { id: "carbonite", qty: 4 }], }, { coords: [1532, 2889], items: [{ id: "boletus", qty: 2 }, { id: "lepiota", qty: 6 }, { id: "boletus", qty: 1 }, { id: "lepiota", qty: 4 }, { id: "chamomile", qty: 4 }] }];

COLLECTION.forEach(o => {
    var map = new Map;
    o.items.forEach(({ id, qty }) => map.set(id, (map.get(id) || 0) + qty));
    o.items = Array.from(map, ([id, qty]) => ({ id, qty }));
});

console.log(COLLECTION);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Ele · Accepted Answer · 2018-03-18 23:14:34Z

You can use the functions forEach and reduce

This approach mutates the original array

var COLLECTION = [  {    "coords":[1335,2525],    "items":[      {id: "boletus",qty: 1},      {id: "lepiota",qty: 3},      {id: "boletus",qty: 2},      {id: "lepiota",qty: 4},      {id: "carbonite",qty: 4},    ],  },  {    "coords":[1532,2889],    "items":[      {id: "boletus",qty: 2},      {id: "lepiota",qty: 6},      {id: "boletus",qty: 1},      {id: "lepiota",qty: 4},      {id: "chamomile",qty: 4},    ],  }];
  
COLLECTION.forEach((o) => {
  o.items = Object.values(o.items.reduce((a, c) => {
    (a[c.id] || (a[c.id] = {id: c.id, qty: 0})).qty += c.qty;
    return a;
  }, {}));
});

console.log(COLLECTION);

.as-console-wrapper { max-height: 100% !important; top: 0; }

If you want to create a new array and keep the original data:

This approach uses the function map to create a new "cloned" array.

var COLLECTION = [  {    "coords":[1335,2525],    "items":[      {id: "boletus",qty: 1},      {id: "lepiota",qty: 3},      {id: "boletus",qty: 2},      {id: "lepiota",qty: 4},      {id: "carbonite",qty: 4},    ],  },  {    "coords":[1532,2889],    "items":[      {id: "boletus",qty: 2},      {id: "lepiota",qty: 6},      {id: "boletus",qty: 1},      {id: "lepiota",qty: 4},      {id: "chamomile",qty: 4},    ] }],
    result = COLLECTION.map(o => o);

result.forEach((o) => {
  o.items = Object.values(o.items.reduce((a, c) => {
    (a[c.id] || (a[c.id] = {id: c.id, qty: 0})).qty += c.qty;
    return a;
  }, {}));
});

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

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