Main examples from Martin Fowler article on Collection Pipeline programming pattern with javascript and underscore.js

CollectionPipeline.js

'use strict';
/**
 * Implementing main examples from Martin Fowler article
 * on Collection Pipeline programming pattern:
 * http://martinfowler.com/articles/collection-pipeline/
 * with #javascript and underscore.js: http://underscorejs.org/
 *
 * tested with nodejs v0.10.32
 *
 * underscore.js is required:
 *  $npm install underscore
 */
var _ = require('underscore');

var articles = [
  {title: 'NoDBA',
    words: 561,
    tags: ['nosql', 'people', 'orm'],
    type: ':bliki'},
  {title: 'Infodeck',
    words: 1145,
    tags: ['nosql', 'writing'],
    type: ':bliki'},
  {title: 'OrmHate',
    words: 1718,
    tags: ['nosql', 'orm'],
    type: ':bliki'},
  {title: 'ruby',
    words: 1313,
    tags: ['ruby'],
    type: ':article'},
  {title: 'DDD_Aggregate',
    words: 482,
    tags: ['nosql', 'ddd'],
    type: ':bliki'}];

// count words _
var result = _.chain(articles).map('words').reduce(function(w, a){return w+a}).value();
console.log('wordcount: ', result);


// count articles by type (as in Fowler's article)
result = _.chain(articles)
        .groupBy('type')
        .map(function(value, key) {return [key, value.length];})
        .object()
        .value();
console.log('articles by type (original): ', result);


// count articles by type (using Underscore's countBy function)
result = _(articles).countBy('type');
console.log('articles by type (_.countBy): ', result);


// count number of articles for each tag
result = _.chain(articles)
            .map(function(article){return _(article.tags).map(function(tag){return [tag, article];})})
            .flatten(true)
            .reduce(function(o, a){o[a[0]] ? o[a[0]].push(a[1]) : o[a[0]] = [a[1]]; return o;}, {})
            .map(function(articleList,tag){return [tag, {'articles': articleList.length, 'words': _.reduce(articleList, function(w, a){return w + a.words}, 0)}];})
            .object()
            .value();
console.log('articles for each tag:', result);