Sum Values of Object in a Array

Question

trying to sum my values from my Object in my Array

I have 3 Objects and in every Object there are two fields where i have values declared:

let items = [
       {
        id: 1, 
        label: 'test', 
        itemname: 'testitem', 
        pieces: 4,
        weight: 0.02
      },
      {
        id: 2, 
        label: 'test', 
        itemname: 'testitem', 
        pieces: 4,
        weight: 0.02
      },
      {
        id: 2, 
        label: 'test', 
        itemname: 'testitem', 
        pieces: 4,
        weight: 0.02
      }
    ];

so if i am right the weight sum would be 0.06 and the sum of the pieces would be 12, both multiplied that would be 0.72, that means i want to multiply the sum of the weight with the sum of the pieces.

i saw examples like this:

const weight = items.reduce((prev, cur) => {
  return prev + (cur.weight * cur.pieces);
}, 0);
console.log(weight);

with this example the total sum would be only 0.24. Could someone help me here out

Edit: @Robby Cornelissen was right with his comment. It was a wrong way of thinking on my part.

Answer 1

If you want the total(sum) weight of all items, you will have to get the weight of each individual item first then add them all together.

const sum = (arr) => {
    return arr.map(item => item.pieces * item.weight).reduce((current, total) => current + total)
}

 let items = [{ id: 1, label: 'test', itemname: 'testitem', pieces: 4, weight: 0.02 }, { id: 2, label: 'test', itemname: 'testitem', pieces: 4, weight: 0.02 }, { id: 2, label: 'test', itemname: 'testitem', pieces: 4, weight: 0.02 } ] const sum = (arr) => { return arr.map(item => item.pieces * item.weight).reduce((current, total) => current + total) } const totalWeight = sum(items) console.log(totalWeight)

Answer 2

You can use forEach to loop through the array, adding up the pieces and weight values:

let pieces = 0; // sum of pieces
let weight = 0; // sum of weight
items.forEach(function(elmt){
    pieces += elmt.pieces;
    weight += elmt.weight;
});

Then multiply pieces * weight :

let total = pieces * weight;
console.log(total);

Answer 3

Using class

 let items=[{id:1,label:"test",itemname:"testitem",pieces:4,weight:.02},{id:2,label:"test",itemname:"testitem",pieces:4,weight:.02},{id:2,label:"test",itemname:"testitem",pieces:4,weight:.02}]; class total { weight = 0; pieces = 0; get product() { return this.weight * this.pieces; } } const totalObj = items.reduce((prev, cur) => { prev.weight += cur.weight; prev.pieces += cur.pieces; return prev; }, new total); console.log(totalObj.product);