Association Rule Mining: Example II (Cont.)

There are four 3-itemsets in C3, the only table in the figure, according to the combination: 
 4C3 = (4!) / (3!×1!) = 4
because there are 4 different items, Beer, Diaper, Milk, and Baby powder, in the L2.

In the above figure, the C3=Null should be L3=Null because the supports of all four 3-itemsets are less than 2/5. For the following figure,
  • The support of the itemset {Diaper, Baby powder} is 2/5=40% because the itemset appears in the Transactions 1 and 2.

  • The support of the itemset {Diaper} is 4/5=80% because the itemset appears in the Transactions 1 to 4.

Therefore, the confidence of the itemset {Diaper, Baby powder} is 40%/80%=50%. For the same reason, Thus, the confidence of the itemset {Baby powder, Diaper} is 40%/40%=100%.