The comparative study of apriori and FP-growth algorithm


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  • Minimum support = 2 C^2 גדול יותר אבל בשלב הבא נהיה קטן .
  • The comparative study of apriori and FP-growth algorithm

    2. 2. ContentsIntroductionLiterature SurveyApriori AlgorithmFP-Growth AlgorithmComparative ResultConclusionReference
    3. 3. Introduction Data Mining: It is the process of discovering interesting patterns (or knowledge) from large amount of data.• Which items are frequently purchased with milk?• Fraud detection: Which types of transactions are likely to be fraudulent, given the demographics and transactional history of a particular customer?• Customer relationship management: Which of my customers are likely to be the most loyal, and which are most likely to leave for a competitor? Data Mining helps extract such information
    4. 4. Introduction (contd.)Why Data Mining?Broadly, the data mining could be useful to answer the queries on :• Forecasting• Classification• Association• Clustering• Making the sequence
    5. 5. Introduction (contd.)Data Mining Applications• Aid to marketing or retailing• Market basket analysis (MBA)• Medicare and health care• Criminal investigation and homeland security• Intrusion detection• Phenomena of “beer and baby diapers” And many more…
    6. 6. Literature SurveyAssociation Rule Mining• Proposed by R. Agrawal in 1993.• It is an important data mining model studied extensively by the database and data mining community.• Initially used for Market Basket Analysis to find how items purchased by customers are related.• Given a set of transactions, find rules that will predict the occurrence of an item based on the occurrences of other items in the transaction
    7. 7. Literature Survey (contd.) Frequent Itemset• Itemset TID Items ▫ A collection of one or more items 1 Bread, Milk  Example: {Milk, Bread, Diaper} 2 Bread, Diaper, Beer, Eggs ▫ k-itemset 3 Milk, Diaper, Beer, Coke  An itemset that contains k items 4 Bread, Milk, Diaper, Beer• Support count (σ) 5 Bread, Milk, Diaper, Coke ▫ Frequency of occurrence of an itemset ▫ E.g. σ({Milk, Bread, Diaper}) = 2• Support ▫ Fraction of transactions that contain an itemset ▫ E.g. s( {Milk, Bread, Diaper} ) = 2/5• Frequent Itemset ▫ An itemset whose support is greater than or equal to a minsup threshold
    8. 8. Literature Survey (contd.)Association Rule• Association Rule ▫ An implication expression of TID Items the form X → Y, where X and 1 Bread, Milk Y are itemsets. 2 Bread, Diaper, Beer, Eggs ▫ Example: 3 Milk, Diaper, Beer, Coke {Milk, Diaper} → {Beer} 4 Bread, Milk, Diaper, Beer• Rule Evaluation Metrics 5 Bread, Milk, Diaper, Coke ▫ Support (s)  Fraction of transactions that Example: contain both X and Y {Milk, Diaper} ⇒ Beer ▫ Confidence (c)  Measures how often items in σ (Milk , Diaper, Beer) 2 Y appear in transactions that s= = = 0.4 contain X. |T| 5 σ (Milk, Diaper, Beer) 2 c= = = 0.67 σ (Milk, Diaper ) 3
    9. 9. Apriori Algorithm• Apriori principle: ▫ If an itemset is frequent, then all of its subsets must also be frequent• Apriori principle holds due to the following property of the support measure: ▫ Support of an itemset never exceeds the support of its subsets ▫ This is known as the anti-monotone property of support
    10. 10. Apriori Algorithm (contd.)The basic steps to mine the frequent elements are as follows:• Generate and test: In this first find the 1-itemset frequent elements L1 by scanning the database and removing all those elements from C which cannot satisfy the minimum support criteria.• Join step: To attain the next level elements Ck join the previous frequent elements by self join i.e. Lk-1*Lk-1 known as Cartesian product of Lk-1 . i.e. This step generates new candidate k-itemsets based on joining Lk-1 with itself which is found in the previous iteration. Let Ck denote candidate k-itemset and Lk be the frequent k-itemset.• Prune step: This step eliminates some of the candidate k-itemsets using the Apriori property. A scan of the database to determine the count of each candidate in Ck would result in the determination of Lk (i.e., all candidates having a count no less than the minimum support count are frequent by definition, and therefore belong to Lk). Step 2 and 3 is repeated until no new candidate set is generated.
    11. 11. Database C^1 L1 TID Set-of- itemsetsTID Items Itemset Support 100 { {1},{3},{4} }100 134 {1} 2 200 { {2},{3},{5} }200 235 {2} 3 300 { {1},{2},{3},{5} }300 1235 {3} 3 400 { {2},{5} }400 25 {5} 3 C2 C^2 L2itemset TID Set-of- itemsets Itemset Support{1 2} 100 { {1 3} } {1 3} 2{1 3} 200 { {2 3},{2 5} {3 5} } {2 3} 3{1 5} 300 { {1 2},{1 3},{1 5}, {2 5} 3{2 3} {2 3}, {2 5}, {3 5} } {3 5} 2{2 5} 400 { {2 5} }{3 5} C^3 L3 C3 TID Set-of- itemsets Itemset Supportitemset 200 { {2 3 5} } {2 3 5} 2{2 3 5} 300 { {2 3 5} }
    12. 12. Apriori Algorithm (contd.)Bottlenecks of Apriori• It is no doubt that Apriori algorithm successfully finds the frequent elements from the database. But as the dimensionality of the database increase with the number of items then:• More search space is needed and I/O cost will increase.• Number of database scan is increased thus candidate generation will increase results in increase in computational cost.
    13. 13. FP-Growth Algorithm FP-Growth: allows frequent itemset discovery without candidate itemset generation. Two step approach: ▫ Step 1: Build a compact data structure called the FP-tree  Built using 2 passes over the data-set. ▫ Step 2: Extracts frequent itemsets directly from the FP-tree
    14. 14. FP-Growth Algorithm (contd.)Step 1: FP-Tree Construction FP-Tree is constructed using 2 passes over the data-set:Pass 1: ▫ Scan data and find support for each item. ▫ Discard infrequent items. ▫ Sort frequent items in decreasing order based on their support.• Minimum support count = 2• Scan database to find frequent 1-itemsets• s(A) = 8, s(B) = 7, s(C) = 5, s(D) = 5, s(E) = 3• 􀁺 Item order (decreasing support): A, B, C, D, E Use this order when building the FP- Tree, so common prefixes can be shared.
    15. 15. FP-Growth Algorithm (contd.)Step 1: FP-Tree ConstructionPass 2:Nodes correspond to items and have a counter1. FP-Growth reads 1 transaction at a time and maps it to a path2. Fixed order is used, so paths can overlap when transactions share items (when they have the same prefix ). ▫ In this case, counters are incremented3. Pointers are maintained between nodes containing the same item, creating singly linked lists (dotted lines) ▫ The more paths that overlap, the higher the compression. FP-tree may fit in memory.4. Frequent itemsets extracted from the FP-Tree.
    16. 16. FP-Growth Algorithm (contd.)Step 1: FP-Tree Construction (contd.)
    17. 17. FP-Growth Algorithm (contd.)Complete FP-Tree for Sample Transactions
    18. 18. FP-Growth Algorithm (contd.)Step 2: Frequent Itemset Generation FP-Growth extracts frequent itemsets from the FP-tree. Bottom-up algorithm - from the leaves towards the root Divide and conquer: first look for frequent itemsets ending in e, then de, etc. . . then d, then cd, etc. . . First, extract prefix path sub-trees ending in an item(set). (using the linked lists)
    19. 19. FP-Growth Algorithm (contd.)Prefix path sub-trees (Example)
    20. 20. FP-Growth Algorithm (contd.)Example Let minSup = 2 and extract all frequent itemsets containing E.  Obtain the prefix path sub-tree for E:  Check if E is a frequent item by adding the counts along the linked list (dotted line). If so, extract it. ▫ Yes, count =3 so {E} is extracted as a frequent itemset.  As E is frequent, find frequent itemsets ending in e. i.e. DE, CE, BE and AE.  E nodes can now be removed
    21. 21. FP-Growth Algorithm (contd.)Conditional FP-Tree The FP-Tree that would be built if we only consider transactions containing a particular itemset (and then removing that itemset from all transactions). I Example: FP-Tree conditional on e.
    22. 22. FP-Growth Algorithm (contd.)Current Position in Processing
    23. 23. FP-Growth Algorithm (contd.)Obtain T(DE) from T(E) 4. Use the conditional FP-tree for e to find frequent itemsets ending in DE, CE and AE ▫ Note that BE is not considered as B is not in the conditional FP-tree for E.• Support count of DE = 2 (sum of counts of all D’s)• DE is frequent, need to solve: CDE, BDE, ADE if they exist
    24. 24. FP-Growth Algorithm (contd.)Current Position of Processing
    25. 25. FP-Growth Algorithm (contd.)Solving CDE, BDE, ADE • Sub-trees for both CDE and BDE are empty • no prefix paths ending with C or B • Working on ADEADE (support count = 2) is frequentsolving next sub problem CE
    26. 26. FP-Growth Algorithm (contd.)Current Position in Processing
    27. 27. FP-Growth Algorithm (contd.)Solving for Suffix CE CE is frequent (support count = 2)• Work on next sub problems: BE (no support), AE
    28. 28. FP-Growth Algorithm (contd.)Current Position in Processing
    29. 29. FP-Growth Algorithm (contd.)Solving for Suffix AE AE is frequent (support count = 2) Done with AE Work on next sub problem: suffix D
    30. 30. FP-Growth Algorithm (contd.)Found Frequent Itemsets with Suffix E • E, DE, ADE, CE, AE discovered in this order
    31. 31. FP-Growth Algorithm (contd.)Example (contd.)Frequent itemsets found (ordered by suffix and order in which the are found):
    32. 32. Comparative Result
    33. 33. Conclusion It is found that:• FP-tree: a novel data structure storing compressed, crucial information about frequent patterns, compact yet complete for frequent pattern mining.• FP-growth: an efficient mining method of frequent patterns in large Database: using a highly compact FP-tree, divide-and-conquer method in nature.• Both Apriori and FP-Growth are aiming to find out complete set of patterns but, FP-Growth is more efficient than Apriori in respect to long patterns.
    34. 34. References1. Liwu, ZOU, Guangwei, REN, “The data mining algorithm analysis for personalized service,” Fourth International Conference on Multimedia Information Networking and Security, 2012.2. Jun TAN, Yingyong BU and Bo YANG, “An Efficient Frequent Pattern Mining Algorithm”, Sixth International Conference on Fuzzy Systems and Knowledge Discovery, 2009.3. Wei Zhang, Hongzhi Liao, Na Zhao, “Research on the FP Growth Algorithm about Association Rule Mining”, International Seminar on Business and Information Management, 2008.4. S.P Latha, DR. N.Ramaraj. “Algorithm for Efficient Data Mining”. In Proc. Int’ Conf. on IEEE International Computational Intelligence and Multimedia Applications, 2007.
    35. 35. References (contd.)5. Dongme Sun, Shaohua Teng, Wei Zhang, Haibin Zhu. “An Algorithm to Improve the Effectiveness of Apriori”. In Proc. Int’l Conf. on 6th IEEE International Conf. on Cognitive Informatics (ICCI07), 2007.6. Daniel Hunyadi, “Performance comparison of Apriori and FP-Growth algorithms in generating association rules”, Proceedings of the European Computing Conference, 2006.7. By Jiawei Han, Micheline Kamber, “Data mining Concepts and Techniques” Morgan Kaufmann Publishers, 2006.8. Tan P.-N., Steinbach M., and Kumar V. “Introduction to data mining” Addison Wesley Publishers, 2006.
    36. 36. References (contd.)9. Han.J, Pei.J, and Yin. Y. “Mining frequent patterns without candidate generation”. In Proc. ACM-SIGMOD International Conf. Management of Data (SIGMOD), 2000.10. R. Agrawal, Imielinski.t, Swami.A. “Mining Association Rules between Sets of Items in Large Databases”. In Proc. International Conf. of the ACM SIGMOD Conference Washington DC, USA, 1993.