The Best Way To Compute The Average Age Of Cat Owners In Functional Programming

average-age.js

var _ = require( "lodash" );

// Assume a collection that has:
// - age: Number
// - hasCat: Boolean
var people = require( "./people.json" );

// ----------------------------------------------------------------------------------- //
// ----------------------------------------------------------------------------------- //


var reduction = _.reduce(
	people,
	function operator( accumulator, person ) {

		if ( person.hasCat ) {

			accumulator.sum += person.age;
			accumulator.count++;
			accumulator.average = ( accumulator.sum / accumulator.count );
		}

		return( accumulator );

	},
	{
		sum: 0,
		count: 0,
		average: 0
	}
);

console.log( "Average age of cat owner: %s", reduction.average );


// ----------------------------------------------------------------------------------- //
// ----------------------------------------------------------------------------------- //


var averageAge = _.reduce(
	_.pluck(
		_.where(
			people,
			{
				hasCat: true
			}
		),
		"age"
	),
	function operator( average, age, index, collection ) {

		return( average + ( age / collection.length ) );

	},
	0
);

console.log( "Average age of cat owner: %s", averageAge );


// ----------------------------------------------------------------------------------- //
// ----------------------------------------------------------------------------------- //


var catOwners = _.where( people, { hasCat: true } );
var averageAge = ( _.sum( _.pluck( catOwners, "age" ) ) / catOwners.length );

console.log( "Average age of cat owner: %s", averageAge );


// ----------------------------------------------------------------------------------- //
// ----------------------------------------------------------------------------------- //

var averageAge = _.chain( people )
	.where({ hasCat: true })
	.pluck( "age" )
	.reduce(
		function operator( sum, age, index, collection ) {

			return ( index === ( collection.length - 1 ) )
				? ( ( sum + age ) / collection.length )
				: ( sum + age )
			;

		},
		0
	)
	.value()
;

console.log( "Average age of cat owner: %s", averageAge );

best-way.js

console.log( "Average age of cat owner: %s", getAverageAgeOfCatOwners( people ) );