如何对数组中的相同对象求和

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.

Answer 1

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) 

Answer 2

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); 

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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); 

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Answer 3

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); 

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