Class: Evoc::TopK

Inherits:
Object
  • Object
show all
Defined in:
lib/evoc/algorithms/top_k.rb

Class Method Summary collapse

Class Method Details

.expand(rule, expansions, tx_store) ⇒ Object 



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# File 'lib/evoc/algorithms/top_k.rb', line 51

def self.expand(rule,expansions,tx_store)
  expansions.each do |e|
    # only expand rules with items lexically larger than the lhs
    if rule.lhs.all? {|i| e > i}
      expanded_rule = Evoc::Rule.new(lhs: rule.lhs+[e],rhs: rule.rhs,tx_store: tx_store)
      if expanded_rule.m_support.value > @@min_support
        self.save_rule(expanded_rule)
      end
    end
  end
end

.save_rule(r) ⇒ Object 



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# File 'lib/evoc/algorithms/top_k.rb', line 63

def self.save_rule(r)
  key = "#{r.m_support.value.to_f}|#{r.name}"
    #puts "adding rule #{key}"
  @@top_k_rules.push(key,r)
  @@expansion_candidates.push(key,r)
  if @@top_k_rules.size >= @@k
    ##puts "K is #{@@k} rules in #{@@top_k_rules.size}"
    #puts "new rule sup #{r.m_support.value.to_f} min sup is #{@@min_support}"
    if r.m_support.value > @@min_support
      #puts "new rule larger than min sup"
      # remove min sup rules until size is K
      while (@@top_k_rules.size > @@k) && (@@top_k_rules.min_key.to_f == @@min_support)
        min_rule = @@top_k_rules.delete_min
        #puts "ksize #{@@top_k_rules.size} after removing rule #{min_rule}"
      end
      @@min_support = @@top_k_rules.min_key.to_f
      #puts "set min sup to #{@@min_support}"
    else
     #puts "#{"%f" % r.m_support.value.to_f.to_s} not larger than #{@@min_support}"
    end
  end
end

.topk(k:, min:, max:, tx_store:, query:) ⇒ Object 



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# File 'lib/evoc/algorithms/top_k.rb', line 4

def self.topk(k:,min:,max:,tx_store:,query:)
  @@k = k
  @@top_k_rules = Containers::CRBTreeMap.new
  @@expansion_candidates = Containers::CRBTreeMap.new
  @@min_support = 0
  # start with all subsets of size @min in @query
  query.combination(min).each do |antecedent|
    # check if this antecedent has min_support > 0
    changed_in = tx_store.transactions_of_list(antecedent, strict: true)
    if changed_in.size > 0
      consequents = Set.new
      # find all consequents for this antecedent
      changed_in.each do |tx_id| 
        tx = tx_store.get_tx(id:tx_id,id_type: :index)
        # the tx size must be larger than the antecedent size
        # (so that we have items left for the consequent)
        if (tx.size > antecedent.size) 
          (tx.items - query).each {|c| consequents << c}
        end
      end
      consequents.each do |consequent|
        r = Evoc::Rule.new(lhs:antecedent,rhs: [consequent], tx_store: tx_store)
        if r.m_support.value.to_f >= @@min_support
          self.save_rule(r)
        end
      end
    end
  end

  # now expand antecedents
  while !@@expansion_candidates.empty? && (@@expansion_candidates.min_key.to_f >= @@min_support)
    max_candidate = @@expansion_candidates.delete_max
    #puts "expanding #{max_candidate.name} | #{max_candidate.m_support.value}"
    expansions = query - max_candidate.lhs
    # don't make antecedents larger than @max
    #if (most_frequent_rule.lhs.size < max) & !expansions.empty?
    if (max_candidate.lhs.size < max) 
      self.expand(max_candidate,expansions,tx_store)
    end
    # remove all rules with sup < min_sup from candidates
    while !@@expansion_candidates.empty? && (@@expansion_candidates.min_key.to_f < @@min_support)
      @@expansion_candidates.delete_min
    end
  end
  return Evoc::RuleStore.new(@@top_k_rules.map {|k,rule| rule})
end