title: In C#, parse out biweekly sets of dates from a collection of dates?
body: <p>I <a href="https://stackoverflow.com/questions/15170391/parse-out-monthly-items-from-a-collection-of-datetime-objects">recently asked this question</a>, to take a list of datetime objects and parse out:</p>
  
  <ol>
  <li><p><em>Weekly Recurrence:</em> Collections of dates that match the same dayOfWeek, hour, minute to get a set of lists where each item in the list matches that Key where:</p>
  
  <p>Key is concatenation of DayOfWeek + hour + minute</p></li>
  <li><p><em>Monthly Recurrence:</em> Collections of dates that match the same weekOfMonth, dayOfWeek, hour, minute to get a set of lists where each item in the list matches that Key where:</p>
  
  <p>Key is concatenation of WeekOfMonth + DayOfWeek + hour + minute</p></li>
  </ol>
  
  <p>both of these are working great.  </p>
  
  <p>I have an additional requirement now that I am struggling with to support bi weekly recurrence (every other week).  I am trying to figure out the right key to match on that would work as both the other use cases above have logical computed key but can't figure the algorith / key for every other week</p>