assoc-rules1-3

assoc-rules1-3 - 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 r A large set of i t e m s , e.g., things sold in a supermarket. r A large set of b a s k e t s , each of which is a small set of the items, e.g., the things one customer buys on one day. 3 Support r Simplest question: find sets of items that appear “frequently” in the baskets. r S u p p o r t for itemset I = the number of baskets containing all items in I . r Given a support t h r e s h o l d s , sets of items that appear in > baskets are called f r e q u e n t i t e m s e t s . 4 Example : Frequent Itemsets r Items={milk, coke, pepsi, beer, juice}. r 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} r Frequent itemsets: {m}, {c}, {b}, {j}, , {b,c} , {c,j}. {m,b} 5 Applications – (1) r Real market baskets : chain stores keep terabytes of information about what customers buy together. R Tells how typical customers navigate stores, lets them position tempting items. R Suggests tie-in “tricks,” e.g., run sale on diapers and raise the price of beer. r High support needed, or no $$’s. 6 Applications – (2) r Baskets = sentences; items = words in those sentences. R Lets us find words that appear together unusually frequently, i.e., linked concepts. r Baskets = sentences, items = documents containing those sentences. R Items that appear together too often could represent plagiarism. 7 Applications – (3) r Baskets = people; items = genes or blood-chemistry factors. R Has been used to detect combinations of genes that result in diabetes, e. g. R But requires extension : absence of an item needs to be observed as well as presence. 8 Many-Many Relationships r “Market Baskets” is an abstraction that models any many-many relationship between two concepts: “items” and “baskets.” R Items need not be “contained” in baskets....
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assoc-rules1-3 - 1 Association Rules Market Baskets...

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