periodToDateCountOverTime
The periodToDateCountOverTime function calculates the count of a
			dimension or measure for a given time granularity (for instance, a quarter) up to a
			point in time.
Syntax
periodToDateCountOverTime( measure, dateTime, period)
Arguments
- measure
- 
						An aggregated measure that you want to do the calculation 
- dateTime
- 
						The date dimension over which you're computing PeriodOverTime calculations. 
- period
- 
						(Optional) The time period across which you're computing the computation. Granularity of YEARmeansYearToDatecomputation,QuartermeansQuarterToDate, and so on. Valid granularities includeYEAR,QUARTER,MONTH,WEEK,DAY,HOUR,MINUTE, andSECONDS.The default value is the visual's date dimension granularity. 
Example
The following example calculates the count of vendors month over month.
periodToDateCountOverTime(count(vendorid), pickupDatetime, MONTH)
