Class: FieldTest::Experiment

Inherits:
Object
  • Object
show all
Defined in:
lib/field_test/experiment.rb

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(attributes) ⇒ Experiment

Returns a new instance of Experiment.



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# File 'lib/field_test/experiment.rb', line 5

def initialize(attributes)
  attributes = attributes.symbolize_keys
  @id = attributes[:id]
  @name = attributes[:name] || @id.to_s.titleize
  @description = attributes[:description]
  @variants = attributes[:variants]
  @weights = @variants.size.times.map { |i| attributes[:weights].to_a[i] || 1 }
  @winner = attributes[:winner]
  @started_at = Time.zone.parse(attributes[:started_at].to_s) if attributes[:started_at]
  @ended_at = Time.zone.parse(attributes[:ended_at].to_s) if attributes[:ended_at]
  @goals = attributes[:goals] || ["conversion"]
  @use_events = attributes[:use_events]
end

Instance Attribute Details

#description ⇒ Object (readonly)

Returns the value of attribute description.



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# File 'lib/field_test/experiment.rb', line 3

def description
  @description
end

#ended_at ⇒ Object (readonly)

Returns the value of attribute ended_at.



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# File 'lib/field_test/experiment.rb', line 3

def ended_at
  @ended_at
end

#goals ⇒ Object (readonly)

Returns the value of attribute goals.



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# File 'lib/field_test/experiment.rb', line 3

def goals
  @goals
end

#id ⇒ Object (readonly)

Returns the value of attribute id.



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# File 'lib/field_test/experiment.rb', line 3

def id
  @id
end

#name ⇒ Object (readonly)

Returns the value of attribute name.



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# File 'lib/field_test/experiment.rb', line 3

def name
  @name
end

#started_at ⇒ Object (readonly)

Returns the value of attribute started_at.



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# File 'lib/field_test/experiment.rb', line 3

def started_at
  @started_at
end

#variants ⇒ Object (readonly)

Returns the value of attribute variants.



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# File 'lib/field_test/experiment.rb', line 3

def variants
  @variants
end

#weights ⇒ Object (readonly)

Returns the value of attribute weights.



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# File 'lib/field_test/experiment.rb', line 3

def weights
  @weights
end

#winner ⇒ Object (readonly)

Returns the value of attribute winner.



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# File 'lib/field_test/experiment.rb', line 3

def winner
  @winner
end

Class Method Details

.all ⇒ Object 



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# File 'lib/field_test/experiment.rb', line 184

def self.all
  FieldTest.config["experiments"].map do |id, settings|
    FieldTest::Experiment.new(settings.merge(id: id.to_s))
  end
end

.find(id) ⇒ Object

Raises:



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# File 'lib/field_test/experiment.rb', line 177

def self.find(id)
  experiment = all.index_by(&:id)[id.to_s]
  raise FieldTest::ExperimentNotFound unless experiment

  experiment
end

Instance Method Details

#active? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/field_test/experiment.rb', line 165

def active?
  !winner
end

#convert(participants, goal: nil) ⇒ Object 



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# File 'lib/field_test/experiment.rb', line 58

def convert(participants, goal: nil)
  goal ||= goals.first

  participants = FieldTest::Participant.standardize(participants)
  check_participants(participants)
  membership = membership_for(participants)

  if membership
    if membership.respond_to?(:converted)
      membership.converted = true
      membership.save! if membership.changed?
    end

    if use_events?
      FieldTest::Event.create!(
        name: goal,
        field_test_membership_id: membership.id
      )
    end

    true
  else
    false
  end
end

#events ⇒ Object 



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# File 'lib/field_test/experiment.rb', line 88

def events
  FieldTest::Event.joins(:field_test_membership).where(field_test_memberships: {experiment: id})
end

#memberships ⇒ Object 



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# File 'lib/field_test/experiment.rb', line 84

def memberships
  FieldTest::Membership.where(experiment: id)
end

#multiple_goals? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/field_test/experiment.rb', line 92

def multiple_goals?
  goals.size > 1
end

#results(goal: nil) ⇒ Object 



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# File 'lib/field_test/experiment.rb', line 96

def results(goal: nil)
  goal ||= goals.first

  relation = memberships.group(:variant)
  relation = relation.where("created_at >= ?", started_at) if started_at
  relation = relation.where("created_at <= ?", ended_at) if ended_at

  if use_events?
    data = {}
    sql =
      relation.joins("LEFT JOIN field_test_events ON field_test_events.field_test_membership_id = field_test_memberships.id")
        .select("variant, COUNT(DISTINCT participant) AS participated, COUNT(DISTINCT field_test_membership_id) AS converted")
        .where(field_test_events: {name: [goal, nil]})

    FieldTest::Membership.connection.select_all(sql).each do |row|
      data[[row["variant"], true]] = row["converted"].to_i
      data[[row["variant"], false]] = row["participated"].to_i - row["converted"].to_i
    end
  else
    data = relation.group(:converted).count
  end

  results = {}
  variants.each do |variant|
    converted = data[[variant, true]].to_i
    participated = converted + data[[variant, false]].to_i
    results[variant] = {
      participated: participated,
      converted: converted,
      conversion_rate: participated > 0 ? converted.to_f / participated : nil
    }
  end
  case variants.size
  when 1, 2, 3
    total = 0.0

    (variants.size - 1).times do |i|
      c = results.values[i]
      b = results.values[(i + 1) % variants.size]
      a = results.values[(i + 2) % variants.size]

      alpha_a = 1 + a[:converted]
      beta_a = 1 + a[:participated] - a[:converted]
      alpha_b = 1 + b[:converted]
      beta_b = 1 + b[:participated] - b[:converted]
      alpha_c = 1 + c[:converted]
      beta_c = 1 + c[:participated] - c[:converted]

      # TODO calculate this incrementally by caching intermediate results
      prob_winning =
        if variants.size == 2
          cache_fetch ["field_test", "prob_b_beats_a", alpha_b, beta_b, alpha_c, beta_c] do
            Calculations.prob_b_beats_a(alpha_b, beta_b, alpha_c, beta_c)
          end
        else
          cache_fetch ["field_test", "prob_c_beats_a_and_b", alpha_a, beta_a, alpha_b, beta_b, alpha_c, beta_c] do
            Calculations.prob_c_beats_a_and_b(alpha_a, beta_a, alpha_b, beta_b, alpha_c, beta_c)
          end
        end

      results[variants[i]][:prob_winning] = prob_winning
      total += prob_winning
    end

    results[variants.last][:prob_winning] = 1 - total
  end
  results
end

#use_events? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/field_test/experiment.rb', line 169

def use_events?
  if @use_events.nil?
    FieldTest.events_supported?
  else
    @use_events
  end
end

#variant(participants, options = {}) ⇒ Object 



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# File 'lib/field_test/experiment.rb', line 19

def variant(participants, options = {})
  return winner if winner
  return variants.first if options[:exclude]

  participants = FieldTest::Participant.standardize(participants)
  check_participants(participants)
  membership = membership_for(participants) || FieldTest::Membership.new(experiment: id)

  if options[:variant] && variants.include?(options[:variant])
    membership.variant = options[:variant]
  else
    membership.variant ||= weighted_variant
  end

  # upgrade to preferred participant
  membership.participant = participants.first

  if membership.changed?
    begin
      membership.save!

      # log it!
      info = {
        experiment: id,
        variant: membership.variant,
        participant: membership.participant
      }.merge(options.slice(:ip, :user_agent))

      # sorta logfmt :)
      info = info.map { |k, v| v = "\"#{v}\"" if k == :user_agent; "#{k}=#{v}" }.join(" ")
      Rails.logger.info "[field test] #{info}"
    rescue ActiveRecord::RecordNotUnique
      membership = memberships.find_by(participant: participants.first)
    end
  end

  membership.try(:variant) || variants.first
end