private void PrefixSpan()
{
_allSequentialPatterns.Clear();
ProjectedDatabase projectedDatabase = _sequenceDatabase.ConvertToProjectedDatabase();
// Divides the search space according to frequent items and mine each recursively.
for (int i = 0; i < _1LengthSequentialPatterns.Count; ++i)
{
Sequence seqPattern = _1LengthSequentialPatterns[i];
_allSequentialPatterns.Add(seqPattern);
LogPattern(seqPattern);
ProjectedDatabase freqItemProjectedDb = ConstructProjectedDatabase(seqPattern, projectedDatabase);
if (freqItemProjectedDb == null || !freqItemProjectedDb.IsNotEmpty)
{
continue;
}
PrefixSpan(freqItemProjectedDb);
}
}
private ProjectedDatabase ConstructProjectedDatabase(Sequence prefix, ProjectedDatabase sourceProjectedDatabase)
{
var prefixLastItem = prefix.LastItem;
var projectedDatabase = new ProjectedDatabase(prefix);
// The count of sequences in a database which dont have to contains prefix
// and projected database can still contains some sequential pattern.
int minSequencesInProjectedDb = sourceProjectedDatabase.Size - (int)_minSupport;
for (int sid = 0, lastSid = sourceProjectedDatabase.Size; sid < lastSid; sid++)
{
// If sequence contains the last item of a prefix, project sequence and add it to db.
int itemsetIndex;
if ((itemsetIndex = sourceProjectedDatabase[sid].Contains(prefixLastItem)) >= 0)
{
var pseudoSequence = PseudoSequence.MakeProjection(sourceProjectedDatabase[sid], prefix, itemsetIndex);
if (pseudoSequence != null && pseudoSequence.IsNotEmpty)
{
projectedDatabase.Add(pseudoSequence);
continue;
}
}
// If projected database can not contains new sequential pattern stop projection sooner.
if (--minSequencesInProjectedDb < 0)
{
return(null);
}
}
return(projectedDatabase);
}
private void PrefixSpan(ProjectedDatabase projectedDatabase)
{
if (Stopped)
{
return;
}
_sExtensions.Clear();
_iExtensions.Clear();
// Scans projected database once and finds extension items.
projectedDatabase.FindLocalFrequentItems(_minSupport, _sExtensions, _iExtensions);
var newSequentialPatterns = new List <Sequence>();
// Sequence-extension items.
foreach (var pair in _sExtensions.OrderBy(e => e.Key))
{
newSequentialPatterns.Add(
Sequence.CreateNewBySStep(projectedDatabase.Prefix, pair.Key, pair.Value));
}
// Itemset-extension items.
foreach (var pair in _iExtensions.OrderBy(e => e.Key))
{
newSequentialPatterns.Add(
Sequence.CreateNewByIStep(projectedDatabase.Prefix, pair.Key, pair.Value));
}
// Divides the search space and recursively mine the subset of all sequential patterns.
for (int i = 0; i < newSequentialPatterns.Count; ++i)
{
Sequence seqPattern = newSequentialPatterns[i];
_allSequentialPatterns.Add(seqPattern);
LogPattern(seqPattern);
ProjectedDatabase seqPatternProjectedDatabase = ConstructProjectedDatabase(seqPattern, projectedDatabase);
if (seqPatternProjectedDatabase == null || !seqPatternProjectedDatabase.IsNotEmpty)
{
continue;
}
PrefixSpan(seqPatternProjectedDatabase);
}
}
