I have a snapshot fact table with a time grain of monthly and so the measure values are only point in time, not cumulative over time. I need to derive a Previous Year-End value to compare any given month's values to the end of the previous year like so:
| Month | Val1 | PrevYEVal |
| 2014-10 | 101 | 100 |
| 2014-11 | 103 | 100 |
| 2014-12 | 105 | 100 |
| 2015-01 | 110 | 105 |
| 2015-02 | 115 | 105 |
| 2015-03 | 113 | 105 |
...
| 2015-12 | 120 | 105 |
| 2016-01 | 130 | 120 |
etc...
I'm using SSAS and the time dimension table is set up as such with a Year->Quarter->Month->Day hierarchy.
I can find solutions to a previous month, a rolling number of months and getting a YTD cumulative value but this is a straight up point in time to point in time comparison.
I'm trying to use Lag, Ancestor, and/or ParallelPeriod but I can't seem to get the above result set.