BUILDING A PREDICTIVE MODEL AN EXAMPLE OF A PRODUCT RECOMMENDATION ENGINE

Transcription

1 BUILDING A PREDICTIVE MODEL AN EXAMPLE OF A PRODUCT RECOMMENDATION ENGINE Alex Lin Senior Architect Intelligent Mining [email protected]

2 Outline Predictive modeling methodology k-nearest Neighbor (knn) algorithm Singular value decomposition (SVD) method for dimensionality reduction Using a synthetic data set to test and improve your model Experiment and results 2

3 The Business Problem Design product recommender solution that will increase revenue. $$ 3

4 How Do We Increase Revenue? Increase Revenue Increase Conversion Increase Avg. Order Value Increase Unit Price Increase Units / Order 4

5 Example Is this recommendation effective? Increase Unit Price Increase Units / Order 5

6 What am I going to do? 6

7 Predictive Model Framework Data Features ML Algorithm Prediction Output What data? What feature? Which Algorithm? Cross-sell & Up-sell Recommendation 7

8 What Data to Use? Explicit data Ratings Comments Implicit data Order history / Return history Cart events Page views Click-thru Search log In today s talk we only use Order history and Cart events 8

9 Predictive Model Data Features ML Algorithm Prediction Output Order History Cart Events What feature? Which Algorithm? Cross-sell & Up-sell Recommendation 9

10 What Features to Use? We know that a given product tends to get purchased by customers with similar tastes or needs. Use user engagement data to describe a product. users n item user engagement vector 0

11 Data Representation / Features When we merge every item s user engagement vector, we got a m x n item-user matrix users n items m

12 Data Normalization Ensure the magnitudes of the entries in the dataset matrix are appropriate users n items m.52.8 Remove column average so frequent buyers don t dominate the model 2

13 Data Normalization Different engagement data points (Order / Cart / Page View) should have different weights Common normalization strategies: Remove column average Remove row average Remove global mean Z-score Fill-in the null values 3

14 Predictive Model Data Features ML Algorithm Prediction Output Order History Cart Events User engagement vector Which Algorithm? Cross-sell & Up-sell Recommendation Data Normalization 4

15 Which Algorithm? How do we find the items that have similar user engagement data? users n.25 2 items m.25 We can find the items that have similar user engagement vectors with knn algorithm 5

16 k-nearest Neighbor (knn) Find the k items that have the most similar user engagement vectors users n.5 items m.5 Nearest Neighbors of Item 4 = [2,3,] 6

17 Similarity Measure for knn users n items 2 4 Jaccard coefficient: Cosine similarity: sim(a,b) = cos(a,b) = Pearson Correlation: corr(a,b) = = a.5 sim(a,b) = i a b 2 b 2 =.5 (+) (++) + (+++) (+) (r ai r a )(r bi r b ) (r ai r a ) 2 (r i bi r b ) 2 i (*+ 0.5 *) ( ) * ( ) = m a i b i a i b i m a 2 i ( a i ) 2 m b 2 i ( b i ) 2 match _ cols* Dotprod(a,b) sum(a) * sum(b) match _cols* sum(a 2 ) (sum(a)) 2 match _ cols* sum(b 2 ) (sum(b)) 2 7

18 k-nearest Neighbor (knn) feature space 9 7 Item Similarity Measure (cosine similarity) knn k=5 Nearest Neighbors(8) = [9,6,3,,2] 8

19 Predictive Model Ver. : knn Data Features ML Algorithm Prediction Output Order History Cart Events User engagement vector k-nearest Neighbor (knn) Cross-sell & Up-sell Recommendation Data Normalization 9

20 Cosine Similarity Code fragment long i_cnt = 00000; // number of items 00K long u_cnt = ; // number of users 2M double data[i_cnt][u_cnt]; // 00K by 2M dataset matrix (in reality, it needs to be malloc allocation) double norm[i_cnt]; // assume data matrix is loaded // calculate vector norm for each user engagement vector for (i=0; i<i_cnt; i++) { norm[i] = 0; for (f=0; f<u_cnt; f++) { norm[i] += data[i][f] * data [i][f]; }. 00K rows x 00K rows x 2M features --> scalability problem norm[i] = sqrt(norm[i]); kd-tree, Locality sensitive hashing, } MapReduce/Hadoop, Multicore/Threading, Stream Processors // cosine similarity calculation 2. data[i] is high-dimensional and sparse, similarity measures for (i=0; i<i_cnt; i++) { // loop thru 00K are not reliable --> accuracy problem for (j=0; j<i_cnt; j++) { // loop thru 00K This leads us to The SVD dimensionality reduction! dot_product = 0; for (f=0; f<u_cnt; f++) { // loop thru entire user space 2M dot_product += data[i][f] * data[j][f]; } printf( %d %d %lf\n, i, j, dot_product/(norm[i] * norm[j])); } 20 // find the Top K nearest neighbors here.

21 Singular Value Decomposition (SVD) A = U S V T A m x n matrix U m x r matrix S r x r matrix V T r x n matrix items items rank = k k < r users A k = U k S k V k T users users Low rank approx. Item profile is Low rank approx. User profile is U k * S k S k *V k T items 2 Low rank approx. Item-User matrix is U k * S k * S k *V k T

22 Reduced SVD A k = U k S k V k T A k 00K x 2M matrix U k 00K x 3 matrix S k 3 x 3 matrix V k T 3 x 2M matrix items items 0 0 rank = 3 users Descending Singular Values users Low rank approx. Item profile is U k * S k 22

23 SVD Factor Interpretation Singular values plot (rank=52) S 3 x 3 matrix Descending Singular Values More Significant Latent Factors Noises + Others 23 Less Significant

24 SVD Dimensionality Reduction U k * <----- latent factors -----> S k # of users items 3 rank Need to find the most optimal low rank!! 0 24

25 Missing values Difference between 0 and unknown Missing values do NOT appear randomly. Value = (Preference Factors) + (Availability) (Purchased elsewhere) (Navigation inefficiency) etc. Approx. Value = (Preference Factors) +/- (Noise) Modeling missing values correctly will help us make good recommendations, especially when working with an extremely sparse data set 25

26 Singular Value Decomposition (SVD) Use SVD to reduce dimensionality, so neighborhood formation happens in reduced user space SVD helps model to find the low rank approx. dataset matrix, while retaining the critical latent factors and ignoring noise. Optimal low rank needs to be tuned SVD is computationally expensive SVD Libraries: Matlab [U, S, V] = svds(a,256); SVDPACKC SVDLIBC GHAPACK 26

27 Predictive Model Ver. 2: SVD+kNN Data Features ML Algorithm Prediction Output Order History Cart Events User engagement vector k-nearest Neighbors (knn) in reduced space Cross-sell & Up-sell Recommendation Data Normalization SVD 27

28 Synthetic Data Set Why do we use synthetic data set? So we can test our new model in a controlled environment 28

29 Synthetic Data Set 6 latent factors synthetic e-commerce data set Dimension:,000 (items) by 20,000 (users) 6 user preference factors 6 item property factors (non-negative) Txn Set: n = 55,360 sparsity = % Txn+Cart Set: n = 92,985 sparsity = 99.03% Download: user_id item_id type

30 Synthetic Data Set Item property factors K x 6 matrix a b c User preference factors 6 x 20K matrix x y z items Purchase Likelihood score K x 20K matrix X X 2 X 3 X 4 X 5 X 6 X 2 X 22 X 2 X 24 X 25 X 26 X 3 X 32 X 33 X 34 X 35 X 36 X 4 X 42 X 43 X 44 X 45 X 46 X 5 X 52 X 53 X 54 X 55 X 56 users X 32 = (a, b, c). (x, y, z) = a * x + b * y + c * z X 32 = Likelihood of Item 3 being purchased by User 2 30

31 Synthetic Data Set X X 2 X 3 X 4 Based on the distribution, pre-determine # of items purchased by an user (# of item=2) X 5 X 4 X 3 X 4 Sort by Purchase likelihood Score X 2 X 5 From the top, select and skip certain items to create data sparsity. X 3 X 2 X 5 X X User purchased Item 4 and Item 3

32 Experiment Setup Each model (Random / knn / SVD+kNN) will generate top 20 recommendations for each item. Compare model output to the actual top 20 provided by synthetic data set Evaluation Metrics : Precision %: Overlapping of the top 20 between model output and actual (higher the better) Precision = {Found _ Top20_items} {Actual _ Top20_items} {Found _Top20_items} Quality metric: Average of the actual ranking in the model output (lower the better)

33 Experimental Result knn vs. Random (Control) Precision % (higher is better) Quality (Lower is better) 33

34 Experimental Result Precision % of SVD+kNN Recall % (higher is better) Improvement SVD Rank 34

35 Experimental Result Quality of SVD+kNN Quality (Lower is better) Improvement 35 SVD Rank

36 Experimental Result The effect of using Cart data Precision % (higher is better) SVD Rank 36

37 Experimental Result The effect of using Cart data Quality (Lower is better) SVD Rank 37

38 Outline Predictive modeling methodology k-nearest Neighbor (knn) algorithm Singular value decomposition (SVD) method for dimensionality reduction Using a synthetic data set to test and improve your model Experiment and results 38

39 References J.S. Breese, D. Heckerman and C. Kadie, "Empirical Analysis of Predictive Algorithms for Collaborative Filtering," in Proceedings of the Fourteenth Conference on Uncertainity in Artificial Intelligence (UAI 998), 998. B. Sarwar, G. Karypis, J. Konstan and J. Riedl, "Item-based collaborative filtering recommendation algorithms," in Proceedings of the Tenth International Conference on the World Wide Web (WWW 0), pp , 200. B. Sarwar, G. Karypis, J. Konstan, and J. Riedl "Application of Dimensionality Reduction in Recommender System A Case Study" In ACM WebKDD 2000 Web Mining for E-Commerce Workshop Apache Lucene Mahout Cofi: A Java-Based Collaborative Filtering Library 39

40 Thank you Any question or comment? 40