public static ItemsetCollection FindSubsets(Itemset itemset, int n)
{
var subsets = new ItemsetCollection();
var subsetCount = (int)Math.Pow(2, itemset.Count);
for (var i = 0; i < subsetCount; i++)
{
if (n == 0 || GetOnCount(i, itemset.Count) == n)
{
var binary = DecimalToBinary(i, itemset.Count);
var subset = new Itemset();
for (var charIndex = 0; charIndex < binary.Length; charIndex++)
{
if (binary[charIndex] == '1')
{
subset.Add(itemset[charIndex]);
}
}
subsets.Add(subset);
}
}
return(subsets);
}
public static ItemsetCollection DoApriori(ItemsetCollection db, double supportThreshold)
{
var I = db.GetUniqueItems();
var l = new ItemsetCollection(); //resultant large itemsets
var li = new ItemsetCollection(); //large itemset in each iteration
var ci = new ItemsetCollection(); //pruned itemset in each iteration
ci.AddRange(I.Select(item => new Itemset {
item
}));
//first iteration (1-item itemsets)
//next iterations
var k = 2;
while (ci.Count != 0)
{
//set Li from Ci (pruning)
li.Clear();
foreach (var itemset in ci)
{
itemset.Support = db.FindSupport(itemset);
if (itemset.Support >= supportThreshold)
{
li.Add(itemset);
l.Add(itemset);
}
}
//set Ci for next iteration (find supersets of Li)
ci.Clear();
ci.AddRange(Bit.FindSubsets(li.GetUniqueItems(), k)); //get k-item subsets
k += 1;
}
return(l);
}