/// <summary>
/// Creates a new bitmap by S-Step with a given item-bitmap.
/// </summary>
public Bitmap128 CreateNewBySStep(Bitmap128 itemBitmap)
{
// A new bitmap for S-Step will be create by ANDing transformed sequence-bitmap with item-bitmap.
// During creating a new bitmap also counts the support for a new bitmap.
var support = 0;
var newBitmaps = new UInt128[SequencesCount];
var itemBitmaps = itemBitmap._bitmaps;
for (var sid = 0; sid < SequencesCount; ++sid)
{
if (_bitmaps[sid] == 0)
{
continue;
}
var tid = DeBruijn.FirstSetBit(_bitmaps[sid]);
if ((newBitmaps[sid] = (TransformedBitmap[tid] & itemBitmaps[sid])) == 0)
{
continue;
}
++support;
}
return(support > 0 ? new Bitmap128(newBitmaps, support) : null);
}
/// <summary>
/// For a given prefix returns the frequent candidates.
/// </summary>
public List <uint> GetFrequentItems(SeqBitmap prefixBitmap, IList <uint> candidates)
{
int transactions = 0;
var transactionSBitVectors = new byte[
prefixBitmap.Sequences8Count + prefixBitmap.Sequences16Count +
prefixBitmap.Sequences32Count + prefixBitmap.Sequences64Count + prefixBitmap.Sequences128Count][];
if (prefixBitmap.Sequences8Count > 0)
{
var prefixBitmaps8 = prefixBitmap.Bitmaps8;
for (int sid = 0; sid < prefixBitmap.Sequences8Count; sid++)
{
if (prefixBitmaps8[sid] == 0)
{
continue;
}
transactionSBitVectors[transactions++] = _bitVectors8[sid, DeBruijn.FirstSetBit(prefixBitmaps8[sid])];
}
}
if (prefixBitmap.Sequences16Count > 0)
{
var prefixBitmaps16 = prefixBitmap.Bitmaps16;
for (int sid = 0; sid < prefixBitmap.Sequences16Count; sid++)
{
if (prefixBitmaps16[sid] == 0)
{
continue;
}
transactionSBitVectors[transactions++] = _bitVectors16[sid, DeBruijn.FirstSetBit(prefixBitmaps16[sid])];
}
}
if (prefixBitmap.Sequences32Count > 0)
{
var prefixBitmaps32 = prefixBitmap.Bitmaps32;
for (int sid = 0; sid < prefixBitmap.Sequences32Count; sid++)
{
if (prefixBitmaps32[sid] == 0)
{
continue;
}
transactionSBitVectors[transactions++] = _bitVectors32[sid, DeBruijn.FirstSetBit(prefixBitmaps32[sid])];
}
}
if (prefixBitmap.Sequences64Count > 0)
{
var prefixBitmaps64 = prefixBitmap.Bitmaps64;
for (int sid = 0; sid < prefixBitmap.Sequences64Count; sid++)
{
if (prefixBitmaps64[sid] == 0)
{
continue;
}
transactionSBitVectors[transactions++] = _bitVectors64[sid, DeBruijn.FirstSetBit(prefixBitmaps64[sid])];
}
}
if (prefixBitmap.Sequences128Count > 0)
{
var prefixBitmaps128 = prefixBitmap.Bitmaps128;
for (int sid = 0; sid < prefixBitmap.Sequences128Count; sid++)
{
if (prefixBitmaps128[sid] == 0)
{
continue;
}
transactionSBitVectors[transactions++] = _bitVectors128[sid, DeBruijn.FirstSetBit(prefixBitmaps128[sid])];
}
}
var frequetItems = new List <uint>();
for (int i = 0, j = candidates.Count; i < j; i++)
{
var candidate = candidates[i];
int candidateSupport = 0;
for (int tid = 0; tid < transactions; tid++)
{
candidateSupport += transactionSBitVectors[tid][candidate];
if (candidateSupport < _minSupport)
{
continue;
}
frequetItems.Add(candidate);
break;
}
}
return(frequetItems);
}