Thursday, May 25, 2017

Open Source: Frequent Sequential Pattern Mining in Java


Package provides java implementation of sequential pattern mining algorithm GSP

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Overview of GSP

The implementation of the algorithm is based on Srikant & Agrawal, 1996
The algorithm makes multiple passes over the data. The first pass determines the support of each item, that is, the number of data-sequences that include the item. At the end of the first pas, the algorithm knows which items are frequent, that is, have minimum support. Each such item yields a 1-element frequent sequence consisting of that item.
Each subsequent pass starts with a seed set: the frequent sequences found in the previous pass. The seed set is used to generate new potentially frequent sequences, called candidate sequences. Each candidate sequence has one more item than a seed sequence; so all the candidate sequences in a pass will have the same number of items. The support for these candidate sequences is found during the pass over the data. At the end of the pass, the algorithm determines which of the candidate sequences are actually frequent. These frequent candidates become the seed for the next pass.


Add the following dependency to your POM file:


The sample code belows illustrates how to use the GSP to find the frequent sequential pattern in a simple sequence database.
List<Sequence> database = new ArrayList<>();

// Below is 4 sequences of transactions stored in the database 
S1  (1), (1 2 3), (1 3), (4), (3 6)
S2  (1 4), (3), (2 3), (1 5)
S3  (5 6), (1 2), (4 6), (3), (2)
S4  (5), (7), (1 6), (3), (2), (3)

database.add(Sequence.make("1", "1,2,3", "1,3", "4", "3,6"));
database.add(Sequence.make("1,4", "3", "2,3", "1,5"));
database.add(Sequence.make("5,6", "1,2", "4,6", "3", "2"));
database.add(Sequence.make("5", "7", "1,6", "3", "2", "3"));

GSP method = new GSP();
List<String> uniqueItems = new MetaData(database).getUniqueItems();
Sequences result = method.minePatterns(database, uniqueItems, -1);

result.getSequences().stream().forEach(sequence -> {
 System.out.println("sequence: " + sequence);

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