lib/mutually_exclusive_collection.rb in rodders-2.1.0 vs lib/mutually_exclusive_collection.rb in rodders-3.0.0

@@ -1,32 +1,102 @@
-# A collection of mutually exclusive events.
+# A collection of mutually exclusive odds for different outcomes.
+# Includes methods for sports betting arbitrage. Due to the discrete nature
+# of real-world monetary amounts, there may be small rounding errors.
 class MutuallyExclusiveCollection
-  # create a new collection with the given events
-  # @param [Array<FixedOdds>] events the events
-  def initialize(events)
-    @events = events.sort
+  # create a new collection with the given odds
+  # @param [Array<FixedOdds>] mutually_exclusive_outcome_odds the odds for all the mutually exclusive outcomes
+  def initialize(mutually_exclusive_outcome_odds)
+    @mutually_exclusive_outcome_odds = mutually_exclusive_outcome_odds.sort
   end
 
-  # the least likely of the events to occur
-  # @return [FixedOdds] the least likely event
+  # the least likely of the odds to occur
+  # @return [FixedOdds] the least likely odd
   def least_likely
-    @events.first
+    @mutually_exclusive_outcome_odds.first
   end
 
-  # the most likely of the events to occur
-  # @return [FixedOdds] the most likely event
+  # the most likely of the odds to occur
+  # @return [FixedOdds] the most likely odd
   def most_likely
-    @events.last
+    @mutually_exclusive_outcome_odds.last
   end  
 
-  # the events in ascending order of probability
-  # @return [Array<FixedOdds>] events in ascending probability
+  # the odds in ascending order of probability
+  # @return [Array<FixedOdds>] odds in ascending probability
   def in_ascending_probability
-    @events
+    @mutually_exclusive_outcome_odds
   end
 
-  # the events in descending order of probability
-  # @return [Array<FixedOdds>] events in descending probability
+  # the odds in descending order of probability
+  # @return [Array<FixedOdds>] odds in descending probability
   def in_descending_probability
-    @events.reverse
+    @mutually_exclusive_outcome_odds.reverse
   end
+
+  # tells if arbitrage is possible for a collection of odds
+  # @return [Boolean] true if profit can be made regardless
+  # of the outcome, false otherwise
+  def arbitrageable?
+    sum_inverse_outcome < 1
+  end
+
+  # the bookmaker's return rate
+  # @return [Number] the bookmaker's return rate as a percentage
+  def bookmakers_return_rate
+    fs = fractions
+    1 - fs.reduce(:*) / fs.reduce(:+)
+  end
+
+  # hash of the odds and what percentage of the total stake should go on each
+  # @return [Hash<FixedOdds, Number>] hash of odds to percentages
+  def percentages
+    hash = {}
+    @mutually_exclusive_outcome_odds.each {|odds| hash[odds] = 1 / odds.fractional_odds / sum_inverse_outcome }
+    hash
+  end
+
+  # hash of the odds and what stakes to put on each given a total stake
+  # @param [Money] total_stake the money to distribute on the outcomes
+  # @return [Hash<FixedOdds, Money>] hash of odds to stakes
+  def stakes_for_total_stake total_stake
+    hash = {}
+    @mutually_exclusive_outcome_odds.each {|odds| hash[odds] = total_stake / odds.fractional_odds / sum_inverse_outcome }
+    hash
+  end
+
+  # hash of the odds and the stakes needed to make the specified profit
+  # @param (see #stakes_for_total_stake)
+  # @return (see #stakes_for_total_stake)
+  def stakes_for_profit desired_profit
+    stakes_for_total_stake(stake_to_profit(desired_profit))
+  end
+
+  # the stake needed to win the desired profit
+  # @param [Money] desired_profit the profit to gain from arbitrage
+  # @return [Money] the stake necessary to realise the desired profit
+  def stake_to_profit desired_profit
+    desired_profit / profit_percentage
+  end
+
+  # the profit won given the total stake to distribute
+  # @param (see #stakes_for_total_stake)
+  # @return [Money] the profit that can be made from a total stake
+  def profit_on_stake total_stake
+    total_stake * profit_percentage
+  end
+
+  # profit percentage available on this arb
+  # @return [Number] the percentage profit available on the arb
+  def profit_percentage
+    sum = sum_inverse_outcome
+    (1 - sum) / sum
+  end
+
+  private
+    def sum_inverse_outcome
+      fractions.reduce(0) {|sum, n| sum + Rational(1, n) }
+    end
+
+    def fractions
+      @mutually_exclusive_outcome_odds.collect {|o| o.fractional_odds }
+    end
 end
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