public Fingerprint(IEncodedFingerprintSchema schema, float startAt, uint sequenceNumber, byte[] originalPoint)
{
Schema = schema;
StartsAt = startAt;
SequenceNumber = sequenceNumber;
OriginalPoint = originalPoint;
}
public int[] Hash(IEncodedFingerprintSchema schema, int n)
{
if (n > PermutationsCount)
{
throw new ArgumentException("n should not exceed number of available hash functions: " + PermutationsCount);
}
int[][] perms = permutations.GetPermutations();
int[] minHash = new int[n];
for (int i = 0; i < n; i++)
{
minHash[i] = perms[i].Length;
for (int j = 0; j < perms[i].Length; j++)
{
int indexAt = perms[i][j];
if (schema.IsTrueAt(indexAt))
{
minHash[i] = j;
break;
}
}
}
return(minHash);
}
/// <summary>
/// Compute Min Hash signature of a fingerprint
/// </summary>
/// <param name="fingerprint">
/// Fingerprint signature
/// </param>
/// <param name="n">
/// The number of hash functions to use
/// </param>
/// <returns>
/// N-sized sub-fingerprint (length of the permutations number)
/// </returns>
/// <remarks>
/// The basic idea in the Min Hashing scheme is to randomly permute the rows and for each
/// column c(i) compute its hash value h(c(i)) as the index of the first row under the permutation that has a 1 in that column.
/// I.e. http://infolab.stanford.edu/~ullman/mmds/book.pdf s.3.3.4
/// </remarks>
private byte[] ComputeMinHashSignature(IEncodedFingerprintSchema fingerprint, int n)
{
if (n > PermutationsCount)
{
throw new ArgumentException("n should not exceed number of available hash functions: " + PermutationsCount);
}
int[][] perms = permutations.GetPermutations();
byte[] minHash = new byte[n]; /*100*/
for (int i = 0; i < n; i++)
{
minHash[i] = 255; /*The probability of occurrence of 1 after position 255 is very insignificant*/
for (byte j = 0; j < perms[i].Length /*256*/; j++)
{
int indexAt = perms[i][j];
if (fingerprint.IsTrueAt(indexAt))
{
minHash[i] = j; /*Looking for first occurrence of '1'*/
break;
}
}
}
return(minHash); /*Array of 100 elements with bit turned ON if permutation captured successfully a TRUE bit*/
}
public byte[] Hash(IEncodedFingerprintSchema fingerprint, int n)
{
return(ComputeMinHashSignature(fingerprint, n));
}
public Fingerprint(IEncodedFingerprintSchema schema, float startAt, uint sequenceNumber)
{
Schema = schema;
StartsAt = startAt;
SequenceNumber = sequenceNumber;
}
public Fingerprint(IEncodedFingerprintSchema signature, float startAt, uint sequenceNumber)
{
Signature = signature;
StartsAt = startAt;
SequenceNumber = sequenceNumber;
}
