Group & Sum rows using lodash

Question

I'm using the following to process rows from shopping cart. I'm wanting to group the rows and sum the values in the grouping. I'm not able to get the sum to work at all and I was hoping to get some assistance please.

thanks in advance

-- data

var cart: [
      {
        id: 2,
        title: 'Batteries',
        description: 'AAA size batteries',
        price: 10.99
      },
      {
        id: 1,
        title: 'Beacons',
        description: 'Bluetooth long life beacons',
        price: 30.00
      },
      {
        id: 1,
        title: 'Beacons',
        description: 'Bluetooth long life beacons',
        price: 30.00
      }
    ]

-- code

 const groupedResult = _(cart)
    .groupBy('price')
    .map(function(items, price, title) {
      return {
        title: _.map(items, 'title'),
        description: _.map(items, 'description'),
         price: _.sum(price, 'price'),
      };
    }).value()

-- current output

    {title: Array(2), description: Array(2), price: "30"}
    {title: Array(1), description: Array(1), price: "10.99"}

-- expected output

   {title: 'Beacons', description: 'Bluetooth long life beacons', price: '30.00', total: '60.00', quantity: 2}
   {title: 'Batteries', description: 'AAA size batteries', price: '10.99', total: '10.99', quantity: 1}

yes I do. I tried various ways to do this but I kept getting o or undefined for the prices. — Jimi
– Jimi, Commented Mar 5, 2018 at 5:11
guijob I realise this, I thought that I might be able to map the prices and then sum inside the map like : price: ._map(.sum(price, 'price')) — Jimi
– Jimi, Commented Mar 5, 2018 at 5:28

guijob · Accepted Answer · 2018-03-05 05:50:38Z

3

groupBy returns an object instead of an array, but you can get this values using Object.values once you unwrap your result using Array.from(). So, assuming title, description and price with same values for same id, this should work:

 const groupedResult = Object.values(Array.from(_(cart)
 .groupBy('id')))
 .map(x => ({
   title: x[0].title,
   description: x[0].description,
   price: x[0].price,
   quantity: x.length,
   total: _.sumBy(x, x => x.price)
 }));

Note: sumBy is only available in lodash 4.0.0 and above.

edited Mar 5, 2018 at 5:50

answered Mar 5, 2018 at 5:39

guijob

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Comments

Ori Drori · Accepted Answer · 2018-03-05 06:22:33Z

You can reduce the array into a Map, and sum the prices if an id already exists on the Map. Then spread the Map.values() back to an array:

const cart = [{"id":2,"title":"Batteries","description":"AAA size batteries","price":10.99},{"id":1,"title":"Beacons","description":"Bluetooth long life beacons","price":30},{"id":1,"title":"Beacons","description":"Bluetooth long life beacons","price":30}];
    
const result = [...cart.reduce((r, o) => {
  // add a new item to the map, and set price and quantity to 0
  r.has(o.id) || r.set(o.id, Object.assign({}, o, { price: 0, quantity: 0 }));
  
  // get current item;
  const item = r.get(o.id);
  
  // add current price to item
  item.price += o.price;
  
  // increment quantity
  item.quantity++;

  return r;
}, new Map()).values()]; // spread the values iterator back to array

console.log(result);

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