Module: WeightedAverage

Defined in:
lib/weighted_average.rb,
lib/weighted_average/version.rb

Constant Summary collapse

VERSION = 
'1.0.3'

Instance Method Summary collapse

Instance Method Details

#weighted_average(*args) ⇒ Object

Returns a number.



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# File 'lib/weighted_average.rb', line 7

def weighted_average(*args)
  weighted_average = connection.select_value(weighted_average_relation(*args).to_sql, 'weighted_average')
  weighted_average.nil? ? nil : weighted_average.to_f
end

#weighted_average_relation(data_column_names, options = {}) ⇒ Object

Returns the ARel relation for a weighted average query.

Raises:

  • (::ArgumentError) 


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# File 'lib/weighted_average.rb', line 13

def weighted_average_relation(data_column_names, options = {})
  raise ::ArgumentError, "Only use array form if the weighting column in the foreign table is not called 'weighting'" if options[:weighted_by].is_a?(::Array) and options[:weighted_by].length != 2
  raise ::ArgumentError, "No nil values in weighted_by, please" if ::Array.wrap(options[:weighted_by]).any?(&:nil?)

  # :airline_aircraft_seat_class
  association = if options[:weighted_by].present?
    options[:weighted_by].is_a?(::Array) ? reflect_on_association(options[:weighted_by].first.to_sym) : reflect_on_association(options[:weighted_by].to_sym)
  end

  # AirlineAircraftSeatClass
  association_class = association.klass if association
  
  # `airline_aircraft_seat_classes`
  weighted_by_table_name = if association_class
    association_class.quoted_table_name
  else
    quoted_table_name
  end
    
  # `airline_aircraft_seat_classes`.`weighting`
  weighted_by_column_name = if association_class and options[:weighted_by].is_a?(::Array)
    options[:weighted_by].last.to_s
  elsif !association_class and (options[:weighted_by].is_a?(::String) or options[:weighted_by].is_a?(::Symbol))
    options[:weighted_by].to_s
  else
    'weighting'
  end
  weighted_by_column_name = [ weighted_by_table_name, connection.quote_column_name(weighted_by_column_name) ].join '.'
  
  # `aircraft`.`passengers`
  disaggregate_by_column_name = if options[:disaggregate_by]
    [ quoted_table_name, connection.quote_column_name(options[:disaggregate_by]) ].join '.'
  end

  # [ `aircraft`.`foo`, `aircraft`.`baz` ]
  data_column_names = ::Array.wrap(data_column_names).map do |data_column_name|
    [ quoted_table_name, connection.quote_column_name(data_column_name) ].join '.'
  end

  relation = select("(SUM(1.0 * (#{data_column_names.join(' + ')}) #{"/ #{disaggregate_by_column_name} " if disaggregate_by_column_name}* #{weighted_by_column_name}) / SUM(#{weighted_by_column_name})) AS weighted_average")
  data_column_names.each do |data_column_name|
    relation = relation.where("#{data_column_name} IS NOT NULL")
  end

  # avoid division by zero
  relation = relation.where("#{weighted_by_column_name} > 0")
  relation = relation.where("#{disaggregate_by_column_name} > 0") if disaggregate_by_column_name
  
  # FIXME this will break on through relationships, where it has to be :aircraft => :aircraft_class
  relation = relation.joins(association.name) if association_class
  relation
end