PowerBI DAX for Index and Value Change fields

RowIndexAndValueChange

--2018-07-18 Updated to use new RANKX function to deal with duplicate timestamp values.
--
--When there are duplicate timestamp values in the dataset, using the previous method (with EARLIER()) would create
--index values that run, eg, 122, 123, 123, 125, 126.
--Supposing therer were 100 new items per row, and ~5000 total (so total would run 4900, 5000, 5100, 5200, etc),
--the ValueChange would run 100, 100, 5000(!!), 100, 100.
--Now, using a RANKX() with Dense enumeration (https://msdn.microsoft.com/en-us/query-bi/dax/rankx-function-dax),
--we can get dense indices that don't skip, so we can lookup Index-1 and know it always exists.

------------------------------------------

--must be DENSE rank so we can lookup value(rank+1) and not get missing values
Index = RANKX(HangfireSuceeded, HangfireSuceeded[timestamp], HangfireSuceeded[timestamp], ASC, Dense)

--Now with dense rank, HangfireSuceeded[Index]-1 is guaranteed to exist
Value Change = 
   IF (
    HangfireSuceeded[Index] = 1,
    0,
    HangfireSuceeded[value] - LOOKUPVALUE(HangfireSuceeded[value], HangfireSuceeded[Index], HangfireSuceeded[Index]-1)
)