Underscore.JS - countBy method

Syntax

_.countBy(list, iteratee, [context])

countBy method gets the spilted lists count grouped by value returned by the iteratee method provided.

Example

var _ = require('underscore');

var list = [{"title": "Learn Java", "Author": "Sam", "Cost": 200},
   {"title": "Learn Scala", "Author": "Sam", "Cost": 200},
   {"title": "Learn C", "Author": "Julie", "Cost": 200} ]

//Example 1. invoke countBy method to get book count written by Authors
var result = _.countBy(list, 'Author');
console.log(result);

//Example 2. invoke countBy method to get book count by their cost
result = _.countBy(list, 'Cost')
console.log(result)

Save the above program in tester.js. Run the following command to execute this program.

Command

\>node tester.js

Output

{ Sam: 2, Julie: 1 }
{ '200': 3 }