protected boolean hasBackwardExtensionItem(SequenceDatabase<T> sdb) {
List<T> prefix = sdb.getPrefix();
prefix_loop:
for (int i = 0; i < prefix.size(); i++) {
Set<T> intersection = null;
for (Sequence<T> sequence : sdb.getSequences()) {
List<T> mp_i = sequence.getMaximumPeriodOf(prefix, i);
if (mp_i == null || mp_i.isEmpty()) {
continue prefix_loop;
}
if (intersection == null) {
intersection = new HashSet<T>(mp_i);
} else {
intersection.retainAll(mp_i);
if (intersection.isEmpty()) {
continue prefix_loop;
}
}
}
if (logger.isTraceEnabled()) {
logger.trace(
"Open: The prefix can be extended by backward extension items {}, found in each of the {} maximum period.",
intersection,
toOrdinal(i));
}
return true;
}
return false;
}
protected List<List<T>> bide(SequenceDatabase<T> sdb, int minSup, ResultHandler<T> handler) {
List<T> prefix = sdb.getPrefix();
if (prefix != null && backScan(sdb)) {
return Collections.emptyList();
}
SortedMap<T, Integer> frequencies = sdb.getItemFrequencies(minSup);
if (isPrefixClosed(sdb, frequencies)) {
synchronized (handler) {
handler.handle(prefix, sdb.getSupportOfPrefix(), sdb);
}
}
List<List<T>> prefixes = new ArrayList<List<T>>();
for (Map.Entry<T, Integer> entry : frequencies.entrySet()) {
List<T> extendedPrefix = new ArrayList<T>();
if (prefix != null) {
extendedPrefix.addAll(prefix);
}
extendedPrefix.add(entry.getKey());
prefixes.add(extendedPrefix);
}
return prefixes;
}
protected boolean isPrefixClosed(SequenceDatabase<T> sdb, SortedMap<T, Integer> frequencies) {
List<T> prefix = sdb.getPrefix();
if (prefix == null) {
return false;
}
int support = sdb.getSupportOfPrefix();
if (logger.isDebugEnabled()) {
logger.debug("Testing: {}:{}", prefix, support);
}
for (Map.Entry<T, Integer> entry : frequencies.entrySet()) {
if (entry.getValue() == support) {
if (logger.isTraceEnabled()) {
logger.trace(
"Open: The prefix can be extended by a forward extension item {}.", entry.getKey());
}
return false; /* Found a forward extension item */
}
}
if (!hasBackwardExtensionItem(sdb)) {
if (logger.isDebugEnabled()) {
logger.debug("Closed: {}:{}", prefix, support);
}
return true;
}
return false;
}
protected boolean backScan(SequenceDatabase<T> sdb) {
List<T> prefix = sdb.getPrefix();
prefix_loop:
for (int i = 0; i < prefix.size(); i++) {
Set<T> intersection = null;
for (Sequence<T> sequence : sdb.getSequences()) {
List<T> smp_i = sequence.getSemiMaximumPeriodOf(prefix, i);
if (smp_i == null || smp_i.isEmpty()) {
continue prefix_loop;
}
if (intersection == null) {
intersection = new HashSet<T>(smp_i);
} else {
intersection.retainAll(smp_i);
if (intersection.isEmpty()) {
continue prefix_loop;
}
}
}
if (logger.isTraceEnabled()) {
logger.trace(
"Pruned: Search space was pruned by the BackScan method. Items {} exists in each of the {} semi-maximum period.",
intersection,
toOrdinal(i));
}
return true;
}
return false;
}