assoc-rules1-4

assoc-rules1-4 - 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 Market-Baskets (2) Really a general many-many mapping (association) between two kinds of things. But we ask about connections among items, not baskets. The technology focuses on common events , not rare events (long tail). 4 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 . Sometimes given as a percentage. Given a support threshold s , sets of items that appear in at least s baskets are called frequent itemsets . 5 Example : Frequent Itemsets 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}, , {b,c} , {c,j}. {m,b} 6 Applications (1) Items = products; baskets = sets of products someone bought in one trip to the store. Example application : given that many people buy beer and diapers together: Run a sale on diapers; raise price of beer. Only useful if many buy diapers & beer. 7 Applications (2) Baskets = sentences; items = documents containing those sentences. Items that appear together too often could represent plagiarism. Notice items do not have to be in baskets. 8 Applications (3) Baskets = Web pages; items = words. Unusual words appearing together in a large number of documents, e.g., Brad and Angelina, may indicate an interesting relationship. 9 Aside : Words on the Web Many Web-mining applications involve words. 1. Cluster pages by their topic, e.g., sports. 2. Find useful blogs, versus nonsense. 3. Determine the sentiment (positive or negative) of comments....
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This document was uploaded on 03/04/2012.

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assoc-rules1-4 - 1 Association Rules Market Baskets...

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