How to compress duplicate elements and get their quantity values?-CodePudding

I need to find the elements with the same id in the array below, add their amounts and write them in a single line.

 let arr = [
{ itemId: 123, name: '0', quantity: 2 },
{ itemId: 1, name: '1', quantity: 2 },
{ itemId: 13, name: '2', quantity: 2 },
{ itemId: 13, name: '3', quantity: 2 },
{ itemId: 13, name: '4', quantity: 24 },
{ itemId: 13, name: '5', quantity: 2 },
{ itemId: 1, name: '6', quantity: 4 },
{ itemId: 1, name: '7', quantity: 2 },];

I want an output like this:

[{ itemId: 123, name: '1', quantity: 2 },
{ itemId: 1, name: '2', quantity: 6 },
{ itemId: 13, name: '6', quantity: 30 }];

And my code:

const getPureList = () => {
    for (let index = 0; index < arr.length; index  ) {
      for (let a = index   1; a < arr.length; a  ) {
        if (arr[index].itemId === arr[a].itemId) {
          arr[index].quantity  = arr[a].quantity;
          arr.splice(a, 1);
        }
      }
    }
    return arr;
  };

Thanks for your help.

CodePudding user response：

By keeping the name od the first object of the group, you could take an object for grouping and take the values as result.

const
    array = [{ itemId: 123, name: '0', quantity: 2 }, { itemId: 1, name: '1', quantity: 2 }, { itemId: 13, name: '2', quantity: 2 }, { itemId: 13, name: '3', quantity: 2 }, { itemId: 13, name: '4', quantity: 24 }, { itemId: 13, name: '5', quantity: 2 }, { itemId: 1, name: '6', quantity: 4 }, { itemId: 1, name: '7', quantity: 2 }],
    result = Object.values(array.reduce((r, o) => {
        r[o.itemId] ??= { ...o, quantity: 0 };
        r[o.itemId].quantity  = o.quantity;
        return r;
    }, {}));

console.log(result);

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