Add Weighted Average to Aggregate

[Cassandra-Clark]

Weighted average should have two arguments: Value and Weight. Both are columns selected by the user. For each record, Value is multiplied by weight, and the sum of weight is stored. The output value is Sum(Value*Weight)/Sum(Weight)

The API is roughly as follows:

Longest (value:Text|Integer|Any=0) (weight:Text|Integer|Any=1) (as:Text="")

[jdunkerley]

Could also consider adding Concatenate Distinct.