Add common graph use case example: friends recommendation

[kmturley]

Would be good to have an out-of-the-box example of a friends recommendation engine. I've made a quick example here which could be used as a starting point. It could be extended to show things like recommendations based on interests etc.

graph_create.js

let ug = require('ug');
let graph = new ug.Graph();

let users = [
    { id: 1, name: 'Adam' },
    { id: 2, name: 'Beth' },
    { id: 3, name: 'Carl' },
    { id: 4, name: 'Dana' }
];

let locations = [
    { id: 1, name: 'Andora' },
    { id: 2, name: 'Brazil' },
    { id: 3, name: 'Chile' },
    { id: 4, name: 'Dublin' }
];

let likes = [
    { user_id: 1, location_id: 1 },
    { user_id: 1, location_id: 2 },
    { user_id: 2, location_id: 2 },
    { user_id: 2, location_id: 3 },
    { user_id: 3, location_id: 3 }
];

graph.nodes('user').createIndex('id');
graph.nodes('location').createIndex('id');

users.forEach(function (user) {
    graph.createNode('user', user);
});

locations.forEach(function (location) {
    graph.createNode('location', location);
});

likes.forEach(function (like) {
    graph.createEdge('like').link(
        graph.nodes('user').find(like.user_id),
        graph.nodes('location').find(like.location_id)
    ).setDistance(2);
});

graph.save('./users.ugd', function () {
    console.log('created ./users.ugd');
});

graph_load.js

let ug = require('ug');
let graph = new ug.Graph();

let users = [
    { id: 1, name: 'Adam' },
    { id: 2, name: 'Beth' },
    { id: 3, name: 'Carl' },
    { id: 4, name: 'Dana' }
];

graph.load('./users.ugd', function () {
    users.forEach(function (user) {
        let results = graph.closest(graph.nodes('user').find(user.id), {
                compare: function (node) {
                    return node.entity === 'user';
                },
                minDepth: 3,
                count: 1
            }
        );
        let resultNodes = results.map(function (path) {
            return path.end();
        });
        console.log(user.id, user.name);
        console.log(resultNodes);
    });
});