Class: Alf::Aggregator::Variance

Inherits:
Alf::Aggregator show all
Defined in:
lib/alf/aggregator/variance.rb

Overview

Defines a ‘variance()` aggregation operator.

Example:

# direct ruby usage
Alf::Aggregator.variance{ qty }.aggregate(...)

# lispy 
(summarize :supplies, [:sid], :total => variance{ qty })

Direct Known Subclasses

Stddev

Instance Attribute Summary

Attributes inherited from Alf::Aggregator

#functor, #options, #source

Instance Method Summary collapse

Methods inherited from Alf::Aggregator

#==, #aggregate, coerce, #default_options, #happens, #has_source_code!, #infer_type, inherited, #initialize, #to_lispy

Methods included from Support::Registry

#each, #listen, #listeners, #register, #registered

Constructor Details

This class inherits a constructor from Alf::Aggregator

Instance Method Details

#_happens(memo, val) ⇒ Object

Aggregates on a tuple occurence.

See Also:

  • Aggregator::InstanceMethods#_happens


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# File 'lib/alf/aggregator/variance.rb', line 26

def _happens(memo, val) 
  count, mean, m2 = memo
  count += 1
  delta = val - mean
  mean  += (delta / count)
  m2    += delta*(val - mean)
  [count, mean, m2]
end

#finalize(memo) ⇒ Object

Finalizes the computation.

See Also:

  • Aggregator::InstanceMethods#finalize


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# File 'lib/alf/aggregator/variance.rb', line 38

def finalize(memo) 
  count, mean, m2 = memo
  m2 / count
end

#least ⇒ Object

Returns the least value.

See Also:

  • Aggregator::InstanceMethods#least


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# File 'lib/alf/aggregator/variance.rb', line 19

def least()
  [0, 0.0, 0.0]
end