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Java implementation of the Apriori algorithm for mining frequent itemsets
import java.util.*;
/** The class encapsulates an implementation of the Apriori algorithm
* to compute frequent itemsets.
* Datasets contains integers (>=0) separated by spaces, one transaction by line, e.g.
* 1 2 3
* 0 9
* 1 9
* Usage with the command line :
* $ java mining.Apriori fileName support
* $ java mining.Apriori /tmp/data.dat 0.8
* $ java mining.Apriori /tmp/data.dat 0.8 > frequent-itemsets.txt
* For a full library, see SPMF
* @author Martin Monperrus, University of Darmstadt, 2010
* @author Nathan Magnus and Su Yibin, under the supervision of Howard Hamilton, University of Regina, June 2009.
* @copyright GNU General Public License v3
* No reproduction in whole or part without maintaining this copyright notice
* and imposing this condition on any subsequent users.
public class Apriori extends Observable {
public static void main(String[] args) throws Exception {
Apriori ap = new Apriori(args);
/** the list of current itemsets */
private List<int[]> itemsets ;
/** the name of the transcation file */
private String transaFile;
/** number of different items in the dataset */
private int numItems;
/** total number of transactions in transaFile */
private int numTransactions;
/** minimum support for a frequent itemset in percentage, e.g. 0.8 */
private double minSup;
/** by default, Apriori is used with the command line interface */
private boolean usedAsLibrary = false;
/** This is the main interface to use this class as a library */
public Apriori(String[] args, Observer ob) throws Exception
usedAsLibrary = true;
/** generates the apriori itemsets from a file
* @param args configuration parameters: args[0] is a filename, args[1] the min support (e.g. 0.8 for 80%)
public Apriori(String[] args) throws Exception
/** starts the algorithm after configuration */
private void go() throws Exception {
//start timer
long start = System.currentTimeMillis();
// first we generate the candidates of size 1
int itemsetNumber=1; //the current itemset being looked at
int nbFrequentSets=0;
while (itemsets.size()>0)
log("Found "+itemsets.size()+" frequent itemsets of size " + itemsetNumber + " (with support "+(minSup*100)+"%)");;
//display the execution time
long end = System.currentTimeMillis();
log("Execution time is: "+((double)(end-start)/1000) + " seconds.");
log("Found "+nbFrequentSets+ " frequents sets for support "+(minSup*100)+"% (absolute "+Math.round(numTransactions*minSup)+")");
/** triggers actions if a frequent item set has been found */
private void foundFrequentItemSet(int[] itemset, int support) {
if (usedAsLibrary) {
else {System.out.println(Arrays.toString(itemset) + " ("+ ((support / (double) numTransactions))+" "+support+")");}
/** outputs a message in Sys.err if not used as library */
private void log(String message) {
if (!usedAsLibrary) {
/** computes numItems, numTransactions, and sets minSup */
private void configure(String[] args) throws Exception
// setting transafile
if (args.length!=0) transaFile = args[0];
else transaFile = "chess.dat"; // default
// setting minsupport
if (args.length>=2) minSup=(Double.valueOf(args[1]).doubleValue());
else minSup = .8;// by default
if (minSup>1 || minSup<0) throw new Exception("minSup: bad value");
// going thourgh the file to compute numItems and numTransactions
numItems = 0;
BufferedReader data_in = new BufferedReader(new FileReader(transaFile));
while (data_in.ready()) {
String line=data_in.readLine();
if (line.matches("\\s*")) continue; // be friendly with empty lines
StringTokenizer t = new StringTokenizer(line," ");
while (t.hasMoreTokens()) {
int x = Integer.parseInt(t.nextToken());
if (x+1>numItems) numItems=x+1;
/** outputs the current configuration
private void outputConfig() {
//output config info to the user
log("Input configuration: "+numItems+" items, "+numTransactions+" transactions, ");
log("minsup = "+minSup*100+"%");
/** puts in itemsets all sets of size 1,
* i.e. all possibles items of the datasets
private void createItemsetsOfSize1() {
itemsets = new ArrayList<int[]>();
for(int i=0; i<numItems; i++)
int[] cand = {i};
* if m is the size of the current itemsets,
* generate all possible itemsets of size n+1 from pairs of current itemsets
* replaces the itemsets of itemsets by the new ones
private void createNewItemsetsFromPreviousOnes()
// by construction, all existing itemsets have the same size
int currentSizeOfItemsets = itemsets.get(0).length;
log("Creating itemsets of size "+(currentSizeOfItemsets+1)+" based on "+itemsets.size()+" itemsets of size "+currentSizeOfItemsets);
HashMap<String, int[]> tempCandidates = new HashMap<String, int[]>(); //temporary candidates
// compare each pair of itemsets of size n-1
for(int i=0; i<itemsets.size(); i++)
for(int j=i+1; j<itemsets.size(); j++)
int[] X = itemsets.get(i);
int[] Y = itemsets.get(j);
assert (X.length==Y.length);
//make a string of the first n-2 tokens of the strings
int [] newCand = new int[currentSizeOfItemsets+1];
for(int s=0; s<newCand.length-1; s++) {
newCand[s] = X[s];
int ndifferent = 0;
// then we find the missing value
for(int s1=0; s1<Y.length; s1++)
boolean found = false;
// is Y[s1] in X?
for(int s2=0; s2<X.length; s2++) {
if (X[s2]==Y[s1]) {
found = true;
if (!found){ // Y[s1] is not in X
// we put the missing value at the end of newCand
newCand[newCand.length -1] = Y[s1];
// we have to find at least 1 different, otherwise it means that we have two times the same set in the existing candidates
if (ndifferent==1) {
// HashMap does not have the correct "equals" for int[] :-(
// I have to create the hash myself using a String :-(
// I use Arrays.toString to reuse equals and hashcode of String
//set the new itemsets
itemsets = new ArrayList<int[]>(tempCandidates.values());
log("Created "+itemsets.size()+" unique itemsets of size "+(currentSizeOfItemsets+1));
/** put "true" in trans[i] if the integer i is in line */
private void line2booleanArray(String line, boolean[] trans) {
Arrays.fill(trans, false);
StringTokenizer stFile = new StringTokenizer(line, " "); //read a line from the file to the tokenizer
//put the contents of that line into the transaction array
while (stFile.hasMoreTokens())
int parsedVal = Integer.parseInt(stFile.nextToken());
trans[parsedVal]=true; //if it is not a 0, assign the value to true
/** passes through the data to measure the frequency of sets in {@link itemsets},
* then filters thoses who are under the minimum support (minSup)
private void calculateFrequentItemsets() throws Exception
log("Passing through the data to compute the frequency of " + itemsets.size()+ " itemsets of size "+itemsets.get(0).length);
List<int[]> frequentCandidates = new ArrayList<int[]>(); //the frequent candidates for the current itemset
boolean match; //whether the transaction has all the items in an itemset
int count[] = new int[itemsets.size()]; //the number of successful matches, initialized by zeros
// load the transaction file
BufferedReader data_in = new BufferedReader(new InputStreamReader(new FileInputStream(transaFile)));
boolean[] trans = new boolean[numItems];
// for each transaction
for (int i = 0; i < numTransactions; i++) {
// boolean[] trans = extractEncoding1(data_in.readLine());
String line = data_in.readLine();
line2booleanArray(line, trans);
// check each candidate
for (int c = 0; c < itemsets.size(); c++) {
match = true; // reset match to false
// tokenize the candidate so that we know what items need to be
// present for a match
int[] cand = itemsets.get(c);
//int[] cand = candidatesOptimized[c];
// check each item in the itemset to see if it is present in the
// transaction
for (int xx : cand) {
if (trans[xx] == false) {
match = false;
if (match) { // if at this point it is a match, increase the count
//log(Arrays.toString(cand)+" is contained in trans "+i+" ("+line+")");
for (int i = 0; i < itemsets.size(); i++) {
// if the count% is larger than the minSup%, add to the candidate to
// the frequent candidates
if ((count[i] / (double) (numTransactions)) >= minSup) {
//else log("-- Remove candidate: "+ Arrays.toString(candidates.get(i)) + " is: "+ ((count[i] / (double) numTransactions)));
//new candidates are only the frequent candidates
itemsets = frequentCandidates;
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kArTHiCKraJAvel commented Feb 24, 2019

how can i add chess.dat in netbeans?

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K-Wu commented Mar 6, 2019

Thanks so much for sharing! However I found a typo in the code, specifically, line 151

log("minsup = "+minSup+"%");

should be

log("minsup = "+minSup*100+"%");

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monperrus commented Jul 9, 2019

I found a typo in the code, specifically, line 151

Thanks for typo! Fixed.

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monperrus commented Jul 9, 2019

For a full library, see SPMF

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aliakll-cpu commented Jan 11, 2020

i want the same code but only for strings not only integers any help?

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abmustafa commented May 2, 2021

I forked this code and added association rules to it enjoy ;)
My Forked

can you please share your file again? It seems that it doesn't exist anymore

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tomrockdsouza commented Jun 20, 2021

I forked this code and added association rules to it enjoy ;)
My Forked

can you please share your file again? It seems that it doesn't exist anymore

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