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 Authorsvar 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)