VTL-ML - Aggregate and Analytic operators

The following table lists the operators that can be invoked in the Aggregate or in the Analytic invocations described below and their main characteristics.

Operator	Description	Allowed invocations	Type of resulting Measure	Type of operand Measures
count	number of Data Points	Aggregate Analytic	integer	any
min	minimum value of a set of values	Aggregate Analytic	any	any
max	maximum value of a set of values	Aggregate Analytic	any	any
median	median value of a set of numbers	Aggregate Analytic	number	number
sum	sum of a set of numbers	Aggregate Analytic	number or integer	number
avg	average value of a set of numbers	Aggregate Analytic	number	number
stddev_pop	population standard deviation of a set of numbers	Aggregate Analytic	number	number
stddev_samp	sample standard deviation of a set of numbers	Aggregate Analytic	number	number
var_pop	population variance of a set of numbers	Aggregate Analytic	number	number
var_samp	sample variance of a set of numbers	Aggregate Analytic	number	number
first_value	first value in an ordered set of values	Analytic	any	any
last_value	last value in an ordered set of values	Analytic	any	any
lag	in an ordered set of Data Points it returns the value(s) taken from a Data Point at a given physical offset prior to the current Data Point	Analytic	any	any
lead	in an ordered set of Data Points it returns the value(s) taken from a Data Point at a given physical offset beyond the current Data Point	Analytic	any	any
rank	rank (order number) of a Data Point in an ordered set of Data Points	Analytic	integer	any
ratio_to_report	ratio of a value to the sum of a set of values	Analytic	number	number

The column Type of resulting Measure gives the declared super-type of the measure produced by the invocation. The type integer is a subtype of number (see the User Manual). For numeric operators, engines should also document the nominal result type when all operand values are integer:

• count, rank: result is integer.

• min, max: result has the same numeric type as the operand (integer or number).

• sum: result is declared number; when all summed values are integer, the nominal result may remain integer (integer arithmetic, subject to an overflow policy defined by the implementation).

• avg, median, var_*, stddev_*, ratio_to_report: result is number even when operands are integer.

If any operand measure is number (non-integer), or the operator is not closed on integers, the nominal result is number.

• Aggregate invocation
• Analytic invocation
• Counting the number of data points: count
• Minimun value: min
• Maximum value: max
• Median value: median
• Sum: sum
• Average value: avg
• Population standard deviation: stddev_pop
• Sample standard deviation: stddev_samp
• Population variance: var_pop
• Sample variance: var_samp
• First value: first_value
• Last value: last_value
• Lag: lag
• Lead: lead
• Rank: rank
• Ratio to report: ratio_to_report