Frequent Itemset

Synonyms

Frequent set

Definition

Frequent itemsets (Agrawal et al., 1993, 1996) are a form of frequent pattern. Given examples that are sets of items and a minimum frequency, any set of items that occurs at least in the minimum number of examples is a frequent itemset.

For instance, customers of an on-line bookstore could be considered examples, each represented by the set of books he or she has purchased. A set of books, such as {“Machine Learning,” “The Elements of Statistical Learning,” “Pattern Classification,”} is a frequent itemset if it has been bought by sufficiently many customers. Given a frequency threshold, perhaps only 0.1 or 0.01% for an on-line store, all sets of books that have been bought by at least that many customers are called frequent. Discovery of all frequent itemsets is a typical data mining task. The original use has been as part of association rule discovery. Apriori is a classical algorithm for finding frequent itemsets.

The idea generalizes far beyond...