数据挖掘基础:在数据中寻找相关的项目 Apriori算法

Ck: Candidate itemset of size k
Lk : frequent itemset of size k

L1 = {frequent items};
for (k = 1; Lk !=?; k++) do begin
    Ck+1 = candidates generated from Lk;
    for each transaction t in database do
  increment the count of all candidates in Ck+1 that are contained in t
    Lk+1  = candidates in Ck+1 with min_support
    end
return ?k Lk;

SQL应用

Suppose the items in Lk-1 are listed in an order
Step 1: self-joining Lk-1
insert into Ck
select p.item1, p.item2, …, p.itemk-1, q.itemk-1
from Lk-1 p, Lk-1 q
where p.item1=q.item1, …, p.itemk-2=q.itemk-2, p.itemk-1 < q.itemk-1
Step 2: pruning
forall itemsets c in Ck do
forall (k-1)-subsets s of c do
if (s is not in Lk-1) then delete c from Ck