/// <summary>
/// Generate rules from an item set where the rules have a size 1 consequent.
/// Only rules with confidence at least MinConfidence will be returned.
/// </summary>
/// <param name="bElem">The frequent item set to generate rules from</param>
/// <param name="size">The size of the frequent item set.</param>
/// <returns>Rules of the form Y-X -> X where Y is the item set, |X|=1, and confidence(Y-X -> X) >= MinConfidence.</returns>
private IList<AssociationRule> generateSingleConsequentRulesFromItemSet(uint bElem, int size)
{
var rules = new List<AssociationRule>();
for (int i = 0; i < 32; i++) //32 bits in uint
{
uint mask = 1U << i;
if ((bElem & mask) != 0)
{
var rule = new AssociationRule(bElem & ~mask, size - 1, mask, 1, DataSet);
if (rule.Confidence >= MinConfidence)
rules.Add(rule);
}
}
return rules;
}
/// <summary>
/// Generate all rules from frequent itemsets with at least the minimum required confidence.
/// </summary>
/// <param name="freqItemSets">The frequent item sets to generate rules from.</param>
/// <returns>All rules from frequent itemsets with at least the minimum required confidence.</returns>
private IList<AssociationRule> generateRules(Dictionary<int, IList<uint>> freqItemSets)
{
var rules = new List<AssociationRule>();
foreach (int size in freqItemSets.Keys.OrderBy(n => n).Where(n => n >= 2))
{
foreach (uint bElem in freqItemSets[size])
{
//Get rules with size 1 consequents
var startRules = generateSingleConsequentRulesFromItemSet(bElem, size);
rules.AddRange(startRules);
//Genereate rules with larger consequents
for (int conqSize = 2; conqSize < size && startRules.Count > 1; conqSize++)
{
var newRules = new List<AssociationRule>();
//Iterate over pairs of rules with conqSize-1 size consequents.
for (int i = 0; i < startRules.Count - 1; i++)
for (int j = i + 1; j < startRules.Count; j++)
{
AssociationRule rule1 = startRules[i], rule2 = startRules[j];
if (shouldCombine(rule1.Consequent, rule2.Consequent, conqSize - 2)) //Should we combine the consequents?
{
uint conq = rule1.Consequent | rule2.Consequent; //Form new merged consequent.
var rule = new AssociationRule(bElem & ~conq, size - conqSize, conq, conqSize, DataSet);
if (rule.Confidence >= MinConfidence) //Accept the rule if it meets required threshold.
newRules.Add(rule);
}
}
rules.AddRange(newRules);
startRules = newRules; //We will generate the next round of rules from the rules generated this round.
}
}
}
return rules;
}
