/**
* Method to recursively grow a given sequential pattern.
*
* @param prefix the current sequential pattern that we want to try to grow
* @param database the current projected sequence database
* @throws IOException exception if there is an error writing to the output file
*/
private void recursion(SequentialPattern prefix, List<PseudoSequence> database)
throws IOException {
// find frequent items of size 1 in the current projected database.
Set<Pair> pairs = findAllFrequentPairs(prefix, database);
// For each pair found (a pair is an item with a boolean indicating if it
// appears in an itemset that is cut (a postfix) or not, and the sequence IDs
// where it appears in the projected database).
for (Pair pair : pairs) {
// if the item is frequent in the current projected database
if (pair.getCount() >= minsuppAbsolute) {
// create the new postfix by appending this item to the prefix
SequentialPattern newPrefix;
// if the item is part of a postfix
if (pair.isPostfix()) {
// we append it to the last itemset of the prefix
newPrefix = appendItemToPrefixOfSequence(prefix, pair.getItem());
} else { // else, we append it as a new itemset to the sequence
newPrefix = appendItemToSequence(prefix, pair.getItem());
}
// build the projected database with this item
List<PseudoSequence> projectedDB =
buildProjectedContext(pair.getItem(), database, pair.isPostfix());
newPrefix.setSequencesID(pair.getSequencesID());
// save the pattern
savePattern(newPrefix);
// make a recursive call
recursion(newPrefix, projectedDB);
}
}
MemoryLogger.getInstance().checkMemory();
}
/**
* This method creates a copy of the sequence and add a given item to the last itemset of the
* sequence. It sets the support of the sequence as the support of the item.
*
* @param prefix the sequence
* @param item the item
* @return the new sequence
*/
private SequentialPattern appendItemToPrefixOfSequence(SequentialPattern prefix, Integer item) {
SequentialPattern newPrefix = prefix.cloneSequence();
// add to the last itemset
Itemset itemset = newPrefix.get(newPrefix.size() - 1);
itemset.addItem(item);
return newPrefix;
}
/**
* This method saves a sequential pattern to the output file or in memory, depending on if the
* user provided an output file path or not when he launched the algorithm
*
* @param prefix the pattern to be saved.
* @throws IOException exception if error while writing the output file.
*/
private void savePattern(SequentialPattern prefix) throws IOException {
// increase the number of pattern found for statistics purposes
patternCount++;
// if the result should be saved to a file
if (writer != null) {
StringBuffer r = new StringBuffer("");
for (Itemset itemset : prefix.getItemsets()) {
// r.append('(');
for (String item : itemset.getItems()) {
String string = item.toString();
r.append(string);
r.append(' ');
}
r.append("-1 ");
}
//
// // print the list of Pattern IDs that contains this pattern.
// if(prefix.getSequencesID() != null){
// r.append("SID: ");
// for(Integer id : prefix.getSequencesID()){
// r.append(id);
// r.append(' ');
// }
// }
r.append(" #SUP: ");
r.append(prefix.getSequencesID().size());
writer.write(r.toString());
writer.newLine();
} // otherwise the result is kept into memory
else {
patterns.addSequence(prefix, prefix.size());
}
}
/**
* This is the main method for the PrefixSpan algorithm that is called to start the algorithm
*
* @param outputFilePath an output file path if the result should be saved to a file or null if
* the result should be saved to memory.
* @param database a sequence database
* @throws IOException exception if an error while writing the output file
*/
private void prefixSpan(SequenceDatabase database, String outputFilePath) throws IOException {
// if the user want to keep the result into memory
if (outputFilePath == null) {
writer = null;
patterns = new SequentialPatterns("FREQUENT SEQUENTIAL PATTERNS");
} else { // if the user want to save the result to a file
patterns = null;
writer = new BufferedWriter(new FileWriter(outputFilePath));
}
// We have to scan the database to find all frequent patterns of size 1.
// We note the sequences in which these patterns appear.
Map<String, Set<Integer>> mapSequenceID = findSequencesContainingItems(database);
// WE CONVERT THE DATABASE ITON A PSEUDO-DATABASE, AND REMOVE
// THE ITEMS OF SIZE 1 THAT ARE NOT FREQUENT, SO THAT THE ALGORITHM
// WILL NOT CONSIDER THEM ANYMORE. (OPTIMIZATION : OCTOBER-08 )
// Create a list of pseudosequence
List<PseudoSequence> initialContext = new ArrayList<PseudoSequence>();
// for each sequence in the database
for (Sequence sequence : database.getSequences()) {
// remove infrequent items
Sequence optimizedSequence = sequence.cloneSequenceMinusItems(mapSequenceID, minsuppAbsolute);
if (optimizedSequence.size() != 0) {
// if the size is > 0, create a pseudo sequence with this sequence
initialContext.add(new PseudoSequence(optimizedSequence, 0, 0));
}
}
// For each item
for (Entry<String, Set<Integer>> entry : mapSequenceID.entrySet()) {
// if the item is frequent (has a support >= minsup)
if (entry.getValue().size() >= minsuppAbsolute) { // if the item is frequent
// build the projected context
String item = entry.getKey();
List<PseudoSequence> projectedContext = buildProjectedContext(item, initialContext, false);
// Create the prefix for the projected context.
SequentialPattern prefix = new SequentialPattern(0);
prefix.addItemset(new Itemset(item));
prefix.setSequencesID(entry.getValue());
// The prefix is a frequent sequential pattern.
// We save it in the result.
savePattern(prefix); // we found a sequence.
// Recursive call !
recursion(prefix, projectedContext);
}
}
}
/**
* This is the "backscan-pruning" strategy described in the BIDE+ paper to avoid extending some
* prefixs that are guaranteed to not generate a closed pattern (see the BIDE+ paper for details).
*
* @param prefix the current prefix
* @return boolean true if we should not extend the prefix
*/
private boolean checkBackScanPruning(SequentialPattern prefix, Set<Integer> sidset) {
//
// See the BIDE+ paper for details about this method.
// For the number of item occurences that can be generated with this prefix:
for (int i = 0; i < prefix.getItemOccurencesTotalCount(); i++) {
Set<Integer> alreadyVisitedSID = new HashSet<Integer>();
// Create a Map of pairs to count the support of items (represented by a pair)
// in the ith semi-maximum periods
Map<PairBIDE, PairBIDE> mapPaires = new HashMap<PairBIDE, PairBIDE>();
// SOME CODE USED BY "findAllFrequentPairsForBackwardExtensionCheck"
Integer itemI = prefix.getIthItem(i); // iPeriod
Integer itemIm1 = null; // iPeriod -1
if (i > 0) {
itemIm1 = prefix.getIthItem(i - 1);
}
// // END NEW
int seqCount = 0;
// int highestSupportUntilNow = -1;
// (1) For each i, we build the list of maximum periods
// for each sequence in the original database
for (int sequenceID : sidset) {
alreadyVisitedSID.add(sequenceID);
PseudoSequenceBIDE sequence = initialDatabase.get(sequenceID);
PseudoSequenceBIDE period =
sequence.getIthSemiMaximumPeriodOfAPrefix(prefix.getItemsets(), i);
if (period != null) {
// // we add it to the list of maximum periods
boolean hasExtension =
findAllFrequentPairsForBackwardExtensionCheck(
alreadyVisitedSID.size(), prefix, period, i, mapPaires, itemI, itemIm1);
if (hasExtension) {
return true;
}
}
}
}
return false;
}
/**
* This is the "backscan-pruning" strategy described in the BIDE+ paper to avoid extending some
* prefixs that are guaranteed to not generate a closed pattern (see the BIDE+ paper for details).
*
* @param prefix the current prefix
* @param projectedContext the projected database
* @return boolean true if we should not extend the prefix
*/
private boolean checkBackScanPruning(
SequentialPattern prefix, List<PseudoSequenceBIDE> projectedContext) {
// DEBUGGIN
if (prefix.size() == 1 && prefix.get(0).get(0) == 5) {
System.out.println("PREFIX 5 ");
}
//
// See the BIDE+ paper for details about this method.
// For the number of item occurences that can be generated with this prefix:
for (int i = 0; i < prefix.getItemOccurencesTotalCount(); i++) {
Set<Integer> alreadyVisitedSID = new HashSet<Integer>();
// Create a Map of pairs to count the support of items (represented by a pair)
// in the ith semi-maximum periods
Map<PairBIDE, PairBIDE> mapPaires = new HashMap<PairBIDE, PairBIDE>();
// SOME CODE USED BY "findAllFrequentPairsForBackwardExtensionCheck"
Integer itemI = prefix.getIthItem(i); // iPeriod
Integer itemIm1 = null; // iPeriod -1
if (i > 0) {
itemIm1 = prefix.getIthItem(i - 1);
}
// // END NEW
// (1) For each i, we build the list of maximum periods
// for each sequence in the original database
for (PseudoSequenceBIDE pseudoSequence : projectedContext) {
int sequenceID = pseudoSequence.sequence.getId();
alreadyVisitedSID.add(pseudoSequence.sequence.getId());
Position currentCutPosition =
new Position(pseudoSequence.firstItemset, pseudoSequence.firstItem);
PseudoSequenceBIDE sequence = initialDatabase.get(sequenceID);
PseudoSequenceBIDE period =
sequence.getIthSemiMaximumPeriodOfAPrefix(prefix.getItemsets(), i, currentCutPosition);
if (period != null) {
// // we add it to the list of maximum periods
boolean hasExtension =
findAllFrequentPairsForBackwardExtensionCheck(
prefix.getAbsoluteSupport(),
prefix,
period,
i,
mapPaires,
itemI,
itemIm1,
currentCutPosition);
if (hasExtension) {
return true;
}
}
}
}
return false;
}
/**
* This method creates a copy of the sequence and add a given item as a new itemset to the
* sequence. It sets the support of the sequence as the support of the item.
*
* @param prefix the sequence
* @param item the item
* @return the new sequence
*/
private SequentialPattern appendItemToSequence(SequentialPattern prefix, Integer item) {
SequentialPattern newPrefix = prefix.cloneSequence(); // isSuffix
newPrefix.addItemset(new Itemset(item));
return newPrefix;
}
/**
* Method to recursively grow a given sequential pattern.
*
* @param prefix the current sequential pattern that we want to try to grow
* @param database the current projected sequence database
* @throws IOException exception if there is an error writing to the output file
*/
private int recursion(SequentialPattern prefix, List<PseudoSequenceBIDE> contexte)
throws IOException {
// find frequent items of size 1 in the current projected database.
Set<PairBIDE> pairs = findAllFrequentPairs(prefix, contexte);
// we will keep tract of the maximum support of patterns
// that can be found with this prefix, to check
// for forward extension when this method returns.
int maxSupport = 0;
// For each pair found (a pair is an item with a boolean indicating if it
// appears in an itemset that is cut (a postfix) or not, and the sequence IDs
// where it appears in the projected database).
for (PairBIDE pair : pairs) {
// if the item is frequent.
if (pair.getCount() >= minsuppAbsolute) {
// create the new postfix by appending this item to the prefix
SequentialPattern newPrefix;
// if the item is part of a postfix
if (pair.isPostfix()) {
// we append it to the last itemset of the prefix
newPrefix = appendItemToPrefixOfSequence(prefix, pair.getItem()); // is =<is, (deltaT,i)>
} else { // else, we append it as a new itemset to the sequence
newPrefix = appendItemToSequence(prefix, pair.getItem());
}
// build the projected database with this item
// long start = System.currentTimeMillis();
List<PseudoSequenceBIDE> projectedContext =
buildProjectedDatabase(
pair.getItem(), contexte, pair.isPostfix(), pair.getSequenceIDs());
// debugProjectDBTime += System.currentTimeMillis() - start;
// create new prefix
newPrefix.setSequenceIDs(pair.getSequenceIDs());
// variable to keep track of the maximum support of extension
// with this item and this prefix
if (projectedContext.size() >= minsuppAbsolute) {
int maxSupportOfSuccessors = 0;
if (!checkBackScanPruning(newPrefix, pair.getSequenceIDs())) {
maxSupportOfSuccessors = recursion(newPrefix, projectedContext); // récursion
}
// check the forward extension for the prefix
// if no forward extension
if (newPrefix.getSequenceIDs().size() != maxSupportOfSuccessors) {
// if there is no backward extension
if (!checkBackwardExtension(newPrefix, pair.getSequenceIDs())) {
// save the pattern
savePattern(newPrefix);
}
}
} else {
if (!checkBackwardExtension(newPrefix, pair.getSequenceIDs())) {
// save the pattern
savePattern(newPrefix);
}
}
// record the largest support of patterns found starting
// with this prefix until now
if (newPrefix.getAbsoluteSupport() > maxSupport) {
maxSupport = newPrefix.getAbsoluteSupport();
}
}
}
return maxSupport; // return the maximum support generated by extension of the prefix
}
/**
* Method to update the support count of item in a maximum period
*
* @param prefix the current prefix
* @param mapPaires
* @param maximum periods a maximum period
* @return a set of pairs indicating the support of items (note that a pair distinguish between
* items in a postfix, prefix...).
*/
protected boolean findAllFrequentPairsForBackwardExtensionCheck(
int seqProcessedCount,
SequentialPattern prefix,
PseudoSequenceBIDE maximumPeriod,
int iPeriod,
Map<PairBIDE, PairBIDE> mapPaires,
Integer itemI,
Integer itemIm1) {
int supportToMatch = prefix.getSequenceIDs().size();
int maxPeriodSize = maximumPeriod.size();
// for each itemset in that period
for (int i = 0; i < maxPeriodSize; i++) {
int sizeOfItemsetAtI = maximumPeriod.getSizeOfItemsetAt(i);
// NEW
boolean sawI = false; // sawI after current position
boolean sawIm1 = false; // sawI-1 before current position
// END NEW
// NEW march 20 2010 : check if I is after current position in current itemset
for (int j = 0; j < sizeOfItemsetAtI; j++) {
Integer item = maximumPeriod.getItemAtInItemsetAt(j, i);
if (item.equals(itemI)) {
sawI = true;
} else if (item > itemI) {
break;
}
}
// END NEW
for (int j = 0; j < sizeOfItemsetAtI; j++) {
Integer item = maximumPeriod.getItemAtInItemsetAt(j, i);
if (itemIm1 != null && item == itemIm1) {
sawIm1 = true;
}
boolean isPrefix = maximumPeriod.isCutAtRight(i);
boolean isPostfix = maximumPeriod.isPostfix(i);
// END NEW
PairBIDE paire = new PairBIDE(isPrefix, isPostfix, item);
if (seqProcessedCount >= minsuppAbsolute) {
// $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
// normal case
if (addPair(mapPaires, maximumPeriod.getId(), paire, supportToMatch)) {
return true;
}
// NEW: special cases
if (sawIm1) {
PairBIDE paire2 = new PairBIDE(isPrefix, !isPostfix, item);
if (addPair(mapPaires, maximumPeriod.getId(), paire2, supportToMatch)) {
return true;
}
}
if (sawI) {
PairBIDE paire2 = new PairBIDE(!isPrefix, isPostfix, item);
if (addPair(mapPaires, maximumPeriod.getId(), paire2, supportToMatch)) {
return true;
}
}
// END NEW
} else { // $$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$
// normal case
addPairWithoutCheck(mapPaires, maximumPeriod.getId(), paire);
// // NEW: special cases
if (sawIm1) {
PairBIDE paire2 = new PairBIDE(isPrefix, !isPostfix, item);
addPairWithoutCheck(mapPaires, maximumPeriod.getId(), paire2);
}
if (sawI) {
PairBIDE paire2 = new PairBIDE(!isPrefix, isPostfix, item);
addPairWithoutCheck(mapPaires, maximumPeriod.getId(), paire2);
}
// END NEW
}
}
}
return false;
}
/**
* Method to check if a prefix has a backward-extension (see Bide+ article for full details). This
* method do it a little bit differently than the BIDE+ article since we iterate with i on
* elements of the prefix instead of iterating with a i on the itemsets of the prefix. But the
* idea is the same!
*
* @param prefix the current prefix
* @return boolean true, if there is a backward extension
*/
private boolean checkBackwardExtension(SequentialPattern prefix, Set<Integer> sidset) {
// System.out.println("======" + prefix);
int totalOccurenceCount = prefix.getItemOccurencesTotalCount();
// For the ith item of the prefix
for (int i = 0; i < totalOccurenceCount; i++) {
Set<Integer> alreadyVisitedSID = new HashSet<Integer>();
// // SOME CODE USED BY "findAllFrequentPairsForBackwardExtensionCheck"
Integer itemI = prefix.getIthItem(i); // iPeriod
Integer itemIm1 = null; // iPeriod -1
if (i > 0) {
itemIm1 = prefix.getIthItem(i - 1);
}
// // END NEW
// Create a Map of pairs to count the support of items (represented by a pair)
// in the ith semi-maximum periods
Map<PairBIDE, PairBIDE> mapPaires = new HashMap<PairBIDE, PairBIDE>();
// (1) For each i, we build the list of maximum periods
// for each sequence in the original database
// int seqCount =0;
int highestSupportUntilNow = -1;
// 1703 pat - 9391 ms
for (int sequenceID : sidset) {
// OPTIMIZATION PART 1== DON'T CHECK THE BACK EXTENSION IF THERE IS NOT ENOUGH SEQUENCE
// LEFT TO FIND AN EXTENSION
// THIS CAN IMPROVE THE PERFORMANCE BY UP TO 30% on FIFA
int remainingSeqID = (sidset.size() - alreadyVisitedSID.size());
if (highestSupportUntilNow != -1
&& highestSupportUntilNow + remainingSeqID < sidset.size()) {
break;
}
alreadyVisitedSID.add(sequenceID);
// if(!alreadyVisitedSID.contains(sequenceID)) {
// seqCount++;
// alreadyVisitedSID.add(sequenceID);
// }
// END OF OPTIMIZATION PART 1 (IT CONTINUES A FEW LINES BELOW...)
PseudoSequenceBIDE sequence = initialDatabase.get(sequenceID);
PseudoSequenceBIDE period = sequence.getIthMaximumPeriodOfAPrefix(prefix.getItemsets(), i);
// if the period is not null
if (period != null) {
boolean hasBackwardExtension =
findAllFrequentPairsForBackwardExtensionCheck(
alreadyVisitedSID.size(), prefix, period, i, mapPaires, itemI, itemIm1);
if (hasBackwardExtension) {
// System.out.println(prefix + " has a backward extension from " + i + "th
// maxperiod in sequence from seq. " + sequenceID );
return true;
}
// ===== OPTIMIZATION PART 2
if ((sidset.size() - alreadyVisitedSID.size()) < minsuppAbsolute) {
for (PairBIDE pair : mapPaires.values()) {
int supportOfPair = pair.getSequenceIDs().size();
if (supportOfPair > highestSupportUntilNow) {
highestSupportUntilNow =
supportOfPair; // +1 because it may be raised for this sequence...
}
}
}
// ===== END OF OPTIMIZATION PART 2
}
}
}
// totaltimeForBackwardExtension += System.currentTimeMillis() - start;
return false; // no backward extension, we return false
}
/**
* This is the main method for the BIDE+ algorithm.
*
* @param database a sequence database
* @throws IOException exception if some error occurs while writing the output file.
*/
private void bide(SequenceDatabase database, String outputFilePath) throws IOException {
// if the user want to keep the result into memory
if (outputFilePath == null) {
writer = null;
patterns = new SequentialPatterns("FREQUENT SEQUENTIAL PATTERNS");
} else { // if the user want to save the result to a file
patterns = null;
writer = new BufferedWriter(new FileWriter(outputFilePath));
}
// The algorithm first scan the database to find all frequent items
// The algorithm note the sequences in which these items appear.
// This is stored in a map: Key: item Value : IDs of sequences containing the item
Map<Integer, Set<Integer>> mapSequenceID = findSequencesContainingItems(database);
// WE CONVERT THE DATABASE TO A PSEUDO-DATABASE, AND REMOVE
// THE ITEMS OF SIZE 1 THAT ARE NOT FREQUENT, SO THAT THE ALGORITHM
// WILL NOT CONSIDER THEM ANYMORE.
// OPTIMIZATION Create COOC MAP
// coocMapBefore = new HashMap<Integer, Map<Integer,
// Integer>>(mapSequenceID.entrySet().size());
// we create a database
initialDatabase = new ArrayList<PseudoSequenceBIDE>();
// for each sequence of the original database
for (Sequence sequence : database.getSequences()) {
// we make a copy of the sequence while removing infrequent items
Sequence optimizedSequence = sequence.cloneSequenceMinusItems(mapSequenceID, minsuppAbsolute);
if (optimizedSequence.size() != 0) {
// if this sequence has size >0, we add it to the new database
initialDatabase.add(new PseudoSequenceBIDE(optimizedSequence, 0, 0));
}
// // update COOC map
// HashSet<Integer> alreadySeen = new HashSet<Integer>();
// for(List<Integer> itemset : optimizedSequence.getItemsets()) {
// for(Integer item : itemset) {
// Map<Integer, Integer> mapCoocItem = coocMapBefore.get(item);
// if(mapCoocItem == null) {
// mapCoocItem = new HashMap<Integer, Integer>();
// coocMapBefore.put(item, mapCoocItem);
// }
// for(Integer itemSeen : alreadySeen) {
// if(itemSeen != item) {
// Integer frequency = mapCoocItem.get(itemSeen);
// if(frequency == null) {
// mapCoocItem.put(itemSeen, 1);
// }else {
// mapCoocItem.put(itemSeen, frequency+1);
// }
// }
// }
// alreadySeen.add(item);
// }
// }
}
// For each frequent item
loop1:
for (Entry<Integer, Set<Integer>> entry : mapSequenceID.entrySet()) {
// if the item is frequent
if (entry.getValue().size() >= minsuppAbsolute) {
// Map<Integer, Integer> mapCoocItem = coocMapBefore.get(entry.getKey());
// if(mapCoocItem != null) {
// for(Integer supportCoocBefore : mapCoocItem.values()) {
// if(supportCoocBefore >= entry.getValue().size()) {
// continue loop1;
// }
// }
// }
// build the projected database with this item
Integer item = entry.getKey();
List<PseudoSequenceBIDE> projectedContext =
buildProjectedContextSingleItem(item, initialDatabase, false, entry.getValue());
// Create the prefix with this item
SequentialPattern prefix = new SequentialPattern();
prefix.addItemset(new Itemset(item));
// set the sequence IDS of this prefix
prefix.setSequenceIDs(entry.getValue());
// variable to store the largest support of patterns
// that will be found starting with this prefix
if (projectedContext.size() >= minsuppAbsolute) {
int successorSupport = 0;
if (!checkBackScanPruning(prefix, entry.getValue())) {
successorSupport = recursion(prefix, projectedContext); // récursion;
}
// Finally, because this prefix has support > minsup
// and passed the backscan pruning,
// we check if it has no sucessor with support >= minsup
// (a forward extension)
// IF no forward extension
if (successorSupport != entry.getValue().size()) { // ######### MODIFICATION ####
// IF there is also no backward extension
if (!checkBackwardExtension(prefix, entry.getValue())) {
// the pattern is closed and we save it
savePattern(prefix);
}
}
} else {
if (!checkBackwardExtension(prefix, entry.getValue())) {
// the pattern is closed and we save it
savePattern(prefix);
}
}
}
}
// check the memory usage for statistics
MemoryLogger.getInstance().checkMemory();
}
/**
* This method creates a copy of the sequence and add a given item to the last itemset of the
* sequence. It sets the support of the sequence as the support of the item.
*
* @param prefix the sequence
* @param item the item
* @return the new sequence
*/
private SequentialPattern appendItemToPrefixOfSequence(SequentialPattern prefix, String item) {
SequentialPattern newPrefix = prefix.cloneSequence();
Itemset itemset = newPrefix.get(newPrefix.size() - 1);
itemset.addItem(item);
return newPrefix;
}
/**
* This method creates a copy of the sequence and add a given item as a new itemset to the
* sequence. It sets the support of the sequence as the support of the item.
*
* @param prefix the sequence
* @param item the item
* @return the new sequence
*/
private SequentialPattern appendItemToSequence(SequentialPattern prefix, String item) {
SequentialPattern newPrefix = prefix.cloneSequence();
newPrefix.addItemset(new Itemset(item));
return newPrefix;
}
