Frequent Itemsets

Identify frequently bought items (itemsets), filtered based on a minimum user-specified limits, to create rules.

Association rules are calculated from itemsets. If rules are generated from all possible itemsets, there can be a very high number of rules and the rules may not be very meaningful. Also, the model can take a long time to build. Typically it is desirable to only generate rules from itemsets that are well-represented in the data. Frequent itemsets are those that occur with a minimum frequency specified by the user.

The minimum frequent itemset support is a user-specified percentage that limits the number of itemsets used for association rules. An itemset must appear in at least this percentage of all the transactions if it is to be used as a basis for rules.

The following table shows the itemsets from Table 7-7 that are frequent itemsets with support > 66%.

Table 7-8 Frequent Itemsets

Frequent Itemset	Transactions	Support
(B,C)	2 of 3	67%
(B,D)	2 of 3	67%
(B,E)	3 of 3	100%
(C,E)	2 of 3	67%
(D,E)	2 of 3	67%
(B,C,E)	2 of 3	67%
(B,D,E)	2 of 3	67%