SPMF documentation > Mining High-Utility Itemsets in a Transaction Database with Utility Information using the Two-Phase

This example explains how to run the Two-Phase algorithm using the SPMF open-source data mining library.

How to run this example?

What is Two-Phase?

Two-Phase (Liu et al., 2005) is an algorithm for discovering high-utility itemsets in a transaction database containing utility information.

High utility itemset mining has several applications such as discovering groups of items in transactions of a store that generate the most profit. A database containing utility information is a database where items can have quantities and a unit price. Although these algorithms are often presented in the context of market basket analysis, there exist other applications.

What is the input?

Two-phase takes as input a transaction database with utility information and a minimum utility threshold min_utility (a positive integer). Let's consider the following database consisting of 5 transactions (t1,t2...t5) and 7 items (1, 2, 3, 4, 5, 6, 7). This database is provided in the text file "DB_utility.txt" in the package ca.pfv.spmf.tests of the SPMF distribution.


Items Transaction utility Item utilities for this transaction
t1 3 5 1 2 4 6 30 1 3 5 10 6 5
t2 3 5 2 4 20 3 3 8 6
t3 3 1 4 8 1 5 2
t4 3 5 1 7 27 6 6 10 5
t5 3 5 2 7 11 2 3 4 2

Each line of the database is:

Note that the value in the second column for each line is the sum of the values in the third column.

What are real-life examples of such a database? There are several applications in real life. One application is a customer transaction database. Imagine that each transaction represents the items purchased by a customer. The first customer named "t1" bought items 3, 5, 1, 2, 4 and 6. The amount of money spent for each item is respectively 1 $, 3 $, 5 $, 10 $, 6 $ and 5 $. The total amount of money spent in this transaction is 1 + 3 + 5 + 10 + 6 + 5 = 30 $.

What is the output?

The output of Two-Phase is the set of high utility itemsets having a utility no less than a min_utility threshold (a positive integer) set by the user. To explain what is a high utility itemset, it is necessary to review some definitions. An itemset is an unordered set of distinct items. The utility of an itemset in a transaction is the sum of the utility of its items in the transaction. For example, the utility of the itemset {1 4} in transaction t1 is 5 + 6 = 11 and the utility of {1 4} in transaction t3 is 5 + 2 = 7. The utility of an itemset in a database is the sum of its utility in all transactions where it appears. For example, the utility of {1 4} in the database is the utility of {1 4} in t1 plus the utility of {1 4} in t3, for a total of 11 + 7 = 18. A high utility itemset is an itemset such that its utility is no less than min_utility For example, if we run Two Phase with a minimum utility of 30, we obtain 8 high-utility itemsets:

itemsets utility support
{2 4} 30 40 % (2 transactions)
{2 5} 31 60 % (3 transactions)
{1 3 5} 31 40 % (2 transactions)
{2 3 4} 34 40 % (2 transactions)
{2 3 5} 37 60 % (3 transactions)
{2 4 5} 36 40 % (2 transactions)
{2 3 4 5} 40 40 % (2 transactions)
{1 2 3 4 5 6} 30 20 % (1 transactions)

If the database is a transaction database from a store, we could interpret these results as all the groups of items bought together that generated a profit of 30 $ or more.

Input file format

The input file format of Two-phase is defined as follows. It is a text file. Each lines represents a transaction. Each line is composed of three sections, as follows.

For example, for the previous example, the input file is defined as follows:

3 5 1 2 4 6:30:1 3 5 10 6 5
3 5 2 4:20:3 3 8 6
3 1 4:8:1 5 2
3 5 1 7:27:6 6 10 5
3 5 2 7:11:2 3 4 2

Consider the first line. It means that the transaction {3, 5, 1, 2, 4, 6} has a total utility of 30 and that items 3, 5, 1, 2, 4 and 6 respectively have a utility of 1, 3, 5, 10, 6 and 5 in this transaction. The following lines follow the same format.

Output file format

The output file format of Two-phase is defined as follows. It is a text file, where each line represents a high utility itemset. On each line, the items of the itemset are first listed. Each item is represented by an integer, followed by a single space. After, all the items, the keyword "#SUP:" appears, which is followed by a double value indicating the support of the itemset. Then, the keyword " #UTIL: " appears and is followed by the utility of the itemset. For example, we show below the output file for this example.

2 4 #SUP: 0.4 #UTIL: 30
2 5 #SUP: 0.6 #UTIL: 31
1 3 5 #SUP: 0.4 #UTIL: 31
2 3 4 #SUP: 0.4 #UTIL: 34
2 3 5 #SUP: 0.6 #UTIL: 37
2 4 5 #SUP: 0.4 #UTIL: 36
2 3 4 5 #SUP: 0.4 #UTIL: 40
1 2 3 4 5 6 #SUP: 0.2 #UTIL: 30

For example, the first line indicates that the itemset {2, 4} has a support of 0.4 and a utility of 30. The following lines follows the same format.

Performance

High utility itemset mining is a much more difficult problem than frequent itemset mining. Therefore, algorithms for high-utility itemset mining are generally slower than frequent itemset mining algorithms.

The Two-Phase algorithm is an important algorithm because it introduced the concept of mining high utility itemset by using two phases by first overestimating the utility of itemsets in phase I and then calculating their exact utility in phase II. However, there are now some more efficient algorithms. For efficiency, it is recommended to use a more efficient algorithm such as EFIM that is also included in SPMF and is one of the most efficient algorithm for this problem (see performance page of this website).

Implementation details

In the source code version of SPMF, there are two versions of Two-Phase: one that saves the result to a file (MainTestTwoPhaseAlgorithm_saveToFile.java) and one that saves the result to memory (MainTestTwoPhaseAlgorithm_saveToMemory.java). In the graphical interface and command line interface, only the version that saves to file is offered.

Also note that the input format is not exactly the same as described in the original article. But it is equivalent.

Where can I get more information about the Two-Phase algorithm?

Here is an article describing the Two-Phase algorithm:

Y. Liu, W.-K. Liao, A. N. Choudhary: A Two-Phase Algorithm for Fast Discovery of High Utility Itemsets. PAKDD 2005: 689-695

Besides, for a general overview of high utility itemset mining, you may read this survey paper.

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