title: "Average" aggregation of sparsely populated percentage values
body: <p>I have cost center allocation data that is currently fully populated, one record per day, each with one cost center dimension key. The cube has a head count measure (the data is set to "1"), and the aggregate function is set to "LastChild". This means that a head count report will count a person only once in a cost center in any given time period.</p>
  
  <p>Introducing partial allocations - a new measure will have a percentage value for the allocation, allowing for multiple concurrent cost centers where the allocation should add up to 100% (with "day" being the granular level). I am trying to figure out how to configure the aggregation over other time periods. I thought that "Average" should work just fine, i.e. a person who is allocated to a cost center at 50% for half the time period will be reported at 25% for that period.
  The problem that I see is that my facts are not populated for days where the allocation to a cost center was 0%. To illustrate:</p>
  
  <pre><code>Employee1 CostCenterA 1/1/2013 50%
  Employee1 CostCenterB 1/1/2013 50%
  Employee1 CostCenterA 1/2/2013 100%
  Employee1 CostCenterA 1/3/2013 100%
  ... etc with 100% in CostCenterA for all days 
  </code></pre>
  
  <p>The above data on a report by month shows 50% for the allocation to CostCenterB, even though the person was only allocated for one day, and the average percentage on a monthly basis should be 1.6%.</p>
  
  <p>I suppose I could generate the 0%-allocations in the data, but my fact table would explode as a result, so I'd much rather change how the "average" aggregation treats percentage values in facts that are sparsely populated, i.e. the average should be calculated based on the number of granular units in the reporting period (days in the month, in this case 0.5/31), not the number of rows in the fact table (0.5/1).  Can this be done in SSAS?</p>