group_by_date_mongodb.js

/*
 * JavaScript Pretty Date
 * Copyright (c) 2008 John Resig (jquery.com)
 * Licensed under the MIT license.
 */

// Takes an ISO time and returns a string representing how
// long ago the date represents.
function prettyDate(time) {
  var date = time,
    diff = (((new Date()).getTime() - date.getTime()) / 1000),
    day_diff = Math.floor(diff / 86400);
      
  if ( isNaN(day_diff) || day_diff < 0 || day_diff >= 31 )
    return;
      
  return day_diff == 0 && (
      diff < 60 && "just now" ||
      diff < 120 && "1 minute ago" ||
      diff < 3600 && Math.floor( diff / 60 ) + " minutes ago" ||
      diff < 7200 && "1 hour ago" ||
      diff < 86400 && Math.floor( diff / 3600 ) + " hours ago") ||
    day_diff == 1 && "Yesterday" ||
    day_diff < 7 && day_diff + " days ago" ||
    day_diff < 31 && Math.ceil( day_diff / 7 ) + " weeks ago";
} 

var byDay = function(doc) {
  var date = Date.UTC(doc.created_at);
  return { date: date};   
}

var initialDoc = {
  count: 0,
  date: '',
  post_ids: new Array() 
}

var reduce = function(doc, prev) {    
  var prettyDate = function(time) {
    var date = time,
      diff = (((new Date()).getTime() - date.getTime()) / 1000),
      day_diff = Math.floor(diff / 86400);

    if ( isNaN(day_diff) || day_diff < 0 || day_diff >= 31 )
      return;

    return day_diff == 0 && (
        diff < 60 && "just now" ||
        diff < 120 && "1 minute ago" ||
        diff < 3600 && Math.floor( diff / 60 ) + " minutes ago" ||
        diff < 7200 && "1 hour ago" ||
        diff < 86400 && Math.floor( diff / 3600 ) + " hours ago") ||
      day_diff == 1 && "Yesterday" ||
      day_diff < 7 && day_diff + " days ago" ||
      day_diff < 31 && Math.ceil( day_diff / 7 ) + " weeks ago";
  };         
  prev.count          += 1;     
  prev.date            = prettyDate(doc.created_at);        
  prev.post_ids.push(doc._id);         
}

db.events.group({
  keyf:     byDay,
  initial:  initialDoc,
  reduce:  reduce,
  cond:    {created_at: {"$gte": new Date(2010, 0)}},
});