assoc-rules1-2

assoc-rules1-2 - 1 Association Rules Market Baskets...

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Unformatted text preview: 1 Association Rules Market Baskets Frequent Itemsets A-priori Algorithm 2 The Market-Basket Model A large set of items , e.g., things sold in a supermarket. A large set of baskets , each of which is a small set of the items, e.g., the things one customer buys on one day. 3 Support Simplest question: find sets of items that appear frequently in the baskets. Support for itemset I = the number of baskets containing all items in I . Given a support threshold s , sets of items that appear in > s baskets are called frequent itemsets . 4 Example Items={milk, coke, pepsi, beer, juice}. Support = 3 baskets. B 1 = {m, c, b} B 2 = {m, p, j} B 3 = {m, b} B 4 = {c, j} B 5 = {m, p, b} B 6 = {m, c, b, j} B 7 = {c, b, j} B 8 = {b, c} Frequent itemsets: {m}, {c}, {b}, {j}, {m, b}, {c, b}, {j, c}. 5 Applications --- (1) Real market baskets : chain stores keep terabytes of information about what customers buy together. Tells how typical customers navigate stores, lets them position tempting items. Suggests tie-in tricks, e.g., run sale on diapers and raise the price of beer. High support needed, or no $$s . 6 Applications --- (2) Baskets = documents; items = words in those documents. Lets us find words that appear together unusually frequently, i.e., linked concepts. Baskets = sentences, items = documents containing those sentences. Items that appear together too often could represent plagiarism. 7 Applications --- (3) Baskets = Web pages; items = linked pages. Pairs of pages with many common references may be about the same topic. Baskets = Web pages p ; items = pages that link to p . Pages with many of the same links may be mirrors or about the same topic. 8 Important Point Market Baskets is an abstraction that models any many-many relationship between two concepts: items and baskets. Items need not be contained in baskets. Items need not be contained in baskets....
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assoc-rules1-2 - 1 Association Rules Market Baskets...

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