Reduce an array of reviews so that they are grouped by publication

review-reduce.js

db.reviews.find({}, function (err, result) {
  if (err) next(err);

  // each item in the result array looks like this
  // {
  //   source: 'The Washington Post',
  //   location: 'City, State',
  //   review: 'Several paragraphs of review text'
  // }

  // sort publication alphabetically and group
  // by publication
  var reviews = result
    .sort(function (a, b) {
      if (a.source > b.source) return 1;
      if (a.source < b.source) return -1;
      return 0;
    })
    .map(function (item) {
      // return something that looks like the original object
      // but with the review inside an array
      return {
        source: item.source,
        location: item.location,
        reviews: [item.review]
      };
    })
    .reduce(function (prev, curr) {
      // if there was a previous item and the previous item had the same source
      if (prev.length && prev[prev.length - 1].source === curr.source) {
        // add the current review text to the array of reviews
        prev[prev.length - 1].reviews = prev[prev.length - 1].reviews.concat(curr.reviews);
      } else {
        prev.push(curr)
      }
      return prev;
    }, []);
  
  res.render('reviews', reviews);
});

reviews.jade

extends layout
block content
  if (reviews.length)
  h2= review.source
    if (review.location)
      span.review-location= review.location
  each text in review.reviews
    blockquote= text