title: How to group objects with timestamps properties by day, week, month?
body: <p>In a nodejs application, I have an array of event objects formatted as follows:</p>
  
  <pre><code>eventsArray = [ {id: 1, date: 1387271989749 }, {id:2, date: 1387271989760}, ... ]
  </code></pre>
  
  <p>eventsArray having a variable length of n elements, and supposing I choose time reference to be Paris time, I want to be able to group elements by day, week, or month:</p>
  
  <pre><code>groupedByDay = {
  
              2012: { ... },
              2013: {
                dayN  : [{id: a0, date: b0}, {id: a1, date: b1}, {id: a2, date: b2 }],
                dayN+1: [{id: a3, date: b3}, {id: a4, date: b4}, {id: a5, date: b5 }],
                ...
                     },
              2014: { ... }
  
            }
  
  groupedByWeek = {
              2012: { ... }
              2013: {
                weekN: [{id: a0, date: b0}, {id: a1, date: b1}, {id: a2, date: b2 }],
                weekN+1: [{id: a3, date: b3}],
                ....
                    },
               2014: { ... }
                  }
  
  groupedByMonth = {
               2012: { ... },
               2013: {
                 monthN: [ {id: a0, date: b0 }, {id: a1, b1}, {id: a2, b2}, {id: a3, b3 }],
                 monthN+1: [ {id: a4, date: b4 }, {id: a5, b5}, {id: a6, b6}],
                 ...
                     },
                2014: { ... }
                   }
  </code></pre>
  
  <p>Having very little experience with manipulating unix timestamps, I was wondering how this could be done or if there was an npm module that would make this easier.</p>