/// <summary>
/// Encode list of integers to bytes
/// </summary>
/// <param name="postings">a posting list</param>
/// <returns>encoded bytes stream</returns>
public byte[] Encoding(List <Posting> postings)
{
List <int> concat = new List <int>();
//1. Write document frequency
concat.Add(postings.Count);
int previousDocID = 0;
foreach (Posting p in postings)
{
//2. Write docID using gap
concat.Add(p.DocumentId - previousDocID); //4byte integer per docID
List <int> positions = p.Positions;
//3. Write term frequency (# of positions)
concat.Add(positions.Count); //4byte integer per term frequency
//4. Write positions using gap
int previousPos = 0;
foreach (int pos in positions)
{
concat.Add(pos - previousPos); //4byte integer per position
previousPos = pos;
}
previousDocID = p.DocumentId;
}
return(VariableBytes.Compress(concat));
}
/// <summary>
/// Encode list of integers to bytes
/// </summary>
/// <param name="value">List of integers</param>
/// <returns>bytes array</returns>
public byte[] Encoding(List <MaxPriorityQueue.InvertedIndex> queue)
{
queue.Sort(
delegate(MaxPriorityQueue.InvertedIndex Item1, MaxPriorityQueue.InvertedIndex Item2)
{
int docID1 = Item1.GetDocumentId();
int docID2 = Item2.GetDocumentId();
if (docID1 < docID2)
{
return(-1);
}
if (docID2 < docID1)
{
return(1);
}
else
{
return(0);
}
});
List <int> concat = new List <int>();
//1. Write the document frequency
concat.Add(queue.Count);
int previousDocId = 0;
int documentID;
int termFreq;
foreach (MaxPriorityQueue.InvertedIndex item in queue)
{
documentID = item.GetDocumentId();
//1. Write the document id using gaps
concat.Add(documentID - previousDocId);
termFreq = item.GetTermFreq();
//3.Write the term frequency
concat.Add(termFreq);
previousDocId = documentID;
}
return(VariableBytes.Compress(concat));
}
/// <summary>
/// Converts an byte array to a list of postings for a term.
/// The byte array should follow the form
/// < df, (docID tf p1 p2 p3), (doc2 tf p1 p2), ... >
/// </summary>
/// <param name="value"></param>
/// <returns></returns>
public List <Posting> Decoding(byte[] value)
{
List <int> integers = VariableBytes.DecompressToInts(value);
// Read and construct a posting list from bytes from postings.bin
// < df, (docID tf p1 p2 p3), (doc2 tf p1 p2), ... >
// docIDs and positions are written as gap)
List <Posting> postings = new List <Posting>();
int index = 0;
//1. Read document frequency
int docFrequency = integers[index++];
int prevDocID = 0;
for (int i = 0; i < docFrequency; i++) //for each posting
{
//2. Read documentID using gap
int docID = prevDocID + integers[index++];
List <int> positions = new List <int>();
//3. Read term frequency
int termFrequency = integers[index++];
//4. Read positions using gap
int prevPos = 0;
for (int j = 0; j < termFrequency; j++) //for each position
{
int pos = prevPos + integers[index++];
positions.Add(pos);
prevPos = pos; //update prevPos
}
//Insert a posting to the posting list
postings.Add(new Posting(docID, positions));
prevDocID = docID; //update prevDocID
}
return(postings);
}
/// <summary>
/// Decode bytes to Inverted
/// </summary>
/// <param name="value">Bytes</param>
/// <returns>List of integers</returns>
public List <MaxPriorityQueue.InvertedIndex> Decoding(byte[] value)
{
List <int> integers = VariableBytes.DecompressToInts(value);
List <MaxPriorityQueue.InvertedIndex> tierPostings = new List <MaxPriorityQueue.InvertedIndex>();
int index = 0;
int docFrequency = integers[index++];
int previousDocId = 0;
for (int i = 0; i < docFrequency; i++)
{
//Read documentID using gap
int docID = previousDocId + integers[index++];
int termFreq = integers[index++];
tierPostings.Add(new MaxPriorityQueue.InvertedIndex(termFreq, docID));
previousDocId = docID;
}
return(tierPostings);
}
/// <summary>
/// Decode bytes to integers
/// </summary>
/// <param name="value">Bytes</param>
/// <returns>integers</returns>
public int Decoding(byte[] value)
{
return(VariableBytes.Decode(value));
}
/// <summary>
/// Encode integers to bytes
/// </summary>
/// <param name="value">integers</param>
/// <returns>bytes array</returns>
public byte[] Encoding(int value)
{
return(VariableBytes.Encode(value));
}
/// <summary>
/// Decode bytes to list of integers
/// </summary>
/// <param name="value">Bytes</param>
/// <returns>List of integers</returns>
public List <int> Decoding(byte[] value)
{
return(VariableBytes.DecompressToInts(value));
}
/// <summary>
/// Encode list of integers to bytes
/// </summary>
/// <param name="value">List of integers</param>
/// <returns>bytes array</returns>
public byte[] Encoding(List <int> value)
{
return(VariableBytes.Compress(value));
}
