How to sum value in the existing array object based on condition in javascript

Question

I have two array list list1 and list2, property name matches, then sum all the qty of list1 and list2 matched object, return updated qty of list1

function resultantArray(list1, list2){
  let sum = list2.map(o => o.qty|| 0).reduce((a, c) => { return a + c });
   list1.forEach(item=>{      
    list2.find(elm => elm.productcode == item.productcode).qty= sum;
   });
}

var list1 = [
  {id:1, name: "IN",qty: 1},
  {id:2, name: "TH"},
  {id:3, name: "AU"}
]
var list2 = [
  {id:3, name: "IN", qty:1},
  {id:5, name: "IN", qty:1},
  {id:4, name: "TH", qty: 2},
  {id:1, name: "SG", qty: 3}
]

Expected Output:

 [
  {id:1, name: "IN",qty: 3},
  {id:2, name: "TH", qty: 2},
  {id:3, name: "AU"}
]

shouldn't TH be qty 2 in output object?... What happens to items missing by name in list 2? — briosheje
– briosheje, Commented Jun 23, 2020 at 10:27
@briosheje thanks fore reply, i have updated the ouptut, TH should be included, in list2 missing by name also should be included, — codecat
– codecat, Commented Jun 23, 2020 at 10:31
What should happen if in list2 the entry for TH has no qty? What does it mean when there is no qty property? Is it equivalent with qty: 0? — trincot
– trincot, Commented Jun 23, 2020 at 10:55
just a tip, consider including your question on the body of the question, not just on the title. It really makes it more clear what you are looking for. — jpnadas
– jpnadas, Commented Jun 23, 2020 at 11:18

trincot · Accepted Answer · 2020-06-23 11:58:32Z

1

You could create a Map to create the result list, but keyed by name. Then iterate the second list and update the objects in the map accordingly. Finally extract the values into the result list.

The use of the Map avoids that you have use find or filter or some other nested loop, and makes the algorithm run in linear time.

var list1 = [{id:1, name: "IN", qty: 1},{id:2, name: "TH"},{id:3, name: "AU"}]
var list2 = [{id:3, name: "IN", qty:1},{id:5, name: "IN", qty:1},{id:4, name: "TH", qty: 2},{id:1, name: "SG", qty: 3}];

const map = new Map(list1.map(o => [o.name, {...o}]));
for (let o of list2) {
    let p = map.get(o.name);
    if (p && o.qty) p.qty = (p.qty || 0) + o.qty;
}
const result = Array.from(map.values());

console.log(result);

answered Jun 23, 2020 at 11:58

trincot

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Comments

tucuxi · Accepted Answer · 2020-06-23 10:47:43Z

var list1 = [
  {id:1, name: "IN",qty: 1},
  {id:2, name: "TH"},
  {id:3, name: "AU"}
]
var list2 = [
  {id:3, name: "IN", qty:1},
  {id:5, name: "IN", qty:1},
  {id:4, name: "TH", qty: 2},
  {id:1, name: "SG", qty: 3}
]

function process(l1, l2) {
   let qtys = {};
   l1.concat(l2).forEach(o => {
      let q = o.qty || 0;
      if (qtys[o.name] === undefined) {
        qtys[o.name] = o.qty;  // track its qty
      } else {
        qtys[o.name] += o.qty; // add its qty
      }     
   });
   let id = 1;
   return l1.map(o => {
      let r = {id: id++, name: o.name};
      if (qtys[o.name]) r.qty = qtys[o.name];
      return r;
   });
}

console.log(JSON.stringify(process(list1, list2)));

This seems to solve the problem. The first forEach loop adds up all quantities. The second loop constructs the result, looking up only entries in list1. Note that this only works as expected if there are no duplicates in list1.

Rajneesh · Accepted Answer · 2020-06-23 11:20:10Z

0

You can also make use of map function, logic would be to filter the item from second list and get length and add one for being the current element, afterwards if the qty is more than one then record accordingly. Here is the working example:

var list1 = [
  {id:1, name: "IN",qty: 1},
  {id:2, name: "TH"},
  {id:3, name: "AU"}
]
var list2 = [
  {id:3, name: "IN", qty:1},
  {id:5, name: "IN", qty:1},
  {id:4, name: "TH", qty: 2},
  {id:1, name: "SG", qty: 3}
]

var result = list1.map(item=>{
   qty = list2.filter(k=>k.name==item.name).length+1;
   return qty>1 ? {...item, qty} : item;
});

console.log(result);

answered Jun 23, 2020 at 11:20

Rajneesh

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