Quickstart

Reach a working result in a few minutes: filter a list, group it, and total each group — a pattern you can reuse for any array of records.

Prerequisites

Node.js 4.0.0 or later.
A project with a package.json, or a .js file you can run with node.

Install Lodash

bash

npm install lodash

Filter, group, and total

Create a sample dataset

Create orders.js and add a small array of records to work with.

var _ = require('lodash');

var orders = [
  { id: 1, customer: 'ada', status: 'shipped', total: 42.5 },
  { id: 2, customer: 'grace', status: 'pending', total: 17 },
  { id: 3, customer: 'ada', status: 'shipped', total: 8 },
  { id: 4, customer: 'linus', status: 'cancelled', total: 30 },
  { id: 5, customer: 'grace', status: 'shipped', total: 12.25 }
];

Filter with a shorthand predicate

Pass a partial object to _.filter instead of writing a comparison function — lodash treats { status: 'shipped' } as shorthand for order => order.status === 'shipped'.

var shipped = _.filter(orders, { status: 'shipped' });

Group the results

_.groupBy takes a property path and returns an object keyed by that property's values.

var byCustomer = _.groupBy(shipped, 'customer');

Total each group

_.mapValues runs a function over each value of an object and returns a new object with the same keys. sumBy adds up a property across an array of objects.

var totals = _.mapValues(byCustomer, function (customerOrders) {
  return _.sumBy(customerOrders, 'total');
});

console.log(totals);

Run the script

bash

node orders.js

Expected result

{ ada: 50.5, grace: 12.25 }

linus and the pending order do not appear: _.filter already removed every order that was not shipped.

✅If you see { ada: 50.5, grace: 12.25 }, Lodash is installed correctly and you've combined three methods into one working pipeline.

Next steps

Combine steps like these into a single readable pipeline with chain sequences.
See more shorthand forms in Iteratee shorthands and common patterns.
Browse the full API reference organized by category.