Basic Data Mining Technique

Transcription

1 Basic Data Mining Technique

2 What is classification? What is prediction? Supervised and Unsupervised Learning Decision trees Association rule K-nearest neighbor classifier Case-based reasoning Genetic algorithm Rough set approach Fuzzy set approaches Chapter 4 2

3 Chapter 4 3

4 Chapter 4 4

5 Classification: predicts categorical class labels classifies data (constructs a model) based on the training set and the values (class labels) in a classifying attribute and...uses it in classifying new data Prediction: models continuous-valued functions, i.e., predicts unknown or missing values Chapter 4 5

6 Typical Applications credit approval target marketing medical diagnosis treatment effectiveness analysis Chapter 4 6

7 1. Model construction: 2. Model usage: Chapter 4 7

8 1. Model construction: describing a set of predetermined classes Each tuple/sample is assumed to belong to a predefined class, as determined by the class label attribute The set of tuples used for model construction: training set The model is represented as classification rules, decision trees, or mathematical formulae Chapter 4 8

9 Training Data Classification Algorithms N A M E RANK Y E A R S TENURED M ike A ssistant P rof 3 no M ary A ssistant P rof 7 yes B ill P rofessor 2 yes Jim A ssociate P rof 7 yes D ave A ssistant P rof 6 no A nne A ssociate P rof 3 no Classifier (Model) IF rank = professor OR years > 6 THEN tenured = yes Chapter 4 9

10 Classification Process 2. Model usage: for classifying future or unknown objects Estimate accuracy of the model The known label of test sample is compared with the classified result from the model Accuracy rate is the percentage of test set samples that are correctly classified by the model Test set is independent of training set Chapter 4 10

11 Classifier Testing Data Unseen Data (Jeff, Professor, 4) NAM E RANK YEARS TENURED Tom Assistant Prof 2 no M erlisa Associate Prof 7 no G eorge Professor 5 yes Joseph Assistant Prof 7 yes Tenured? Chapter 4 11

12 Prediction is similar to classification 1. Construct a model 2. Use model to predict unknown value Major method for prediction is regression Linear and multiple regression Non-linear regression Prediction is different from classification Classification refers to predict categorical class label Prediction models continuous-valued functions Chapter 4 12

13 1. Data Preparation 2. Evaluating Classification Methods Chapter 4 13

14 Data cleaning Preprocess data in order to reduce noise and handle missing values Relevance analysis (feature selection) Remove the irrelevant or redundant attributes Data transformation Generalize and/or normalize data Chapter 4 14

15 Predictive accuracy Speed and scalability time to construct the model time to use the model Robustness handling noise and missing values Scalability efficiency in disk-resident databases Interpretability: understanding and insight proved by the model Goodness of rules decision tree size compactness of classification rules Chapter 4 15

16 Supervised learning (classification) Supervision: The training data (observations, measurements, etc.) are accompanied by labels indicating the class of the observations New data is classified based on the training set Unsupervised learning (clustering) The class labels of training data is unknown Given a set of measurements, observations, etc. with the aim of establishing the existence of classes or clusters in the data Chapter 4 16

17 Chapter 4 17

18 Chapter 4 18

19 Decision tree A flow-chart-like tree structure Internal node denotes a test on an attribute Branch represents an outcome of the test Leaf nodes represent class labels or class distribution Use of decision tree: Classifying an unknown sample Test the attribute values of the sample against the decision tree Chapter 4 19

20 Decision tree generation consists of two phases 1. Tree construction At start, all the training examples are at the root Partition examples recursively based on selected attributes 2. Tree pruning Identify and remove branches that reflect noise or outliers Chapter 4 20

21 This follows an example from Quinlan s ID3 age income student credit_rating buys_computer <=30 high no fair no <=30 high no excellent no high no fair yes >40 medium no fair yes >40 low yes fair yes >40 low yes excellent no low yes excellent yes <=30 medium no fair no <=30 low yes fair yes >40 medium yes fair yes <=30 medium yes excellent yes medium no excellent yes high yes fair yes >40 medium no excellent no Chapter 4 21

22 age? <=30 overcast >40 student? yes credit rating? no yes fair excellent no yes no yes Chapter 4 22

23 Chapter 4 23

24 Association rule mining: Finding frequent patterns, associations, correlations, or causal structures among sets of items or objects in transaction databases, relational databases, and other information repositories. Applications: Basket data analysis, cross-marketing, catalog design, loss-leader analysis, clustering, classification, etc. Chapter 4 24

25 Chapter 4 25

26 Instance-based learning: Store training examples and delay the processing ( lazy evaluation )...until a new instance must be classified Typical approaches k-nearest neighbor approach Instances represented as points in a Euclidean space. Case-based reasoning Uses symbolic representations and knowledge-based inference Chapter 4 26

27 All instances correspond to points in the n-d space. The nearest neighbor are defined in terms of Euclidean distance. The target function could be discrete- or realvalued. For discrete-valued, the k-nn returns the most common value among the k training examples nearest to xq. Vonoroi diagram: the decision surface induced by _ 1-NN for a typical set of training examples. + _. + + _ xq _ Chapter 4 27

28 Also uses: lazy evaluation + analyze similar instances Difference: Instances... are not points in a Euclidean space Methodology Instances represented by rich symbolic descriptions (e.g., function graphs) Multiple retrieved cases may be combined Chapter 4 28

29 GA: based on an analogy to biological evolution Each rule is represented by a string of bits An initial population is created consisting of randomly generated rules e.g., IF A 1 and Not A 2 then C 2 can be encoded as 100 Based on the notion of survival of the fittest, a new population is formed to consists of the fittest rules and their offsprings The fitness of a rule is represented by its classification accuracy on a set of training examples Offsprings are generated by crossover and mutation Chapter 4 29

30 Chapter 4 30

31 Rough sets are used to approximately or roughly define equivalent classes Chapter 4 31

32 A rough set for a given class C is approximated by two sets: 1. a lower approximation (certain to be in C) and 2. an upper approximation (cannot be described as not belonging to C) Finding the minimal subsets of attributes (for feature reduction) is NPhard Chapter 4 32

33 Fuzzy logic uses truth values between 0.0 and 1.0 to represent the degree of membership (such as using fuzzy membership graph) Fuzzy membeship Low Medium High somewhat low baseline high Income Chapter 4 33

34 Attribute values are converted to fuzzy values e.g., income is mapped into the discrete categories {low, medium, high} with fuzzy values calculated For a given new sample, more than one fuzzy value may apply Each applicable rule contributes a vote for membership in the categories Typically, the truth values for each predicted category are summed Chapter 4 34

35 Data Mining: Concepts and Techniques (Chapter 7 for textbook), Jiawei Han and Micheline Kamber, Intelligent Database Systems Research Lab, School of Computing Science, Simon Fraser University, Canada Chapter 4 35