public static double PearsonCoefficient(GenericVector a, GenericVector b)
{
if (a.Dimensions != b.Dimensions)
{
throw new Exception("Distance can't be computed of vectors with different dimensions");
}
var n = a.Dimensions;
var sigmaA = 0.0;
var sigmaB = 0.0;
var sigmaATimesB = 0.0;
var sigmaASquared = 0.0;
var sigmaBSquared = 0.0;
for (var i = 0; i < a.Dimensions; i++)
{
if (float.IsNaN(a[i]) || float.IsNaN(b[i]))
{
n--;
continue;
}
sigmaA += a[i];
sigmaB += b[i];
sigmaATimesB += a[i] * b[i];
sigmaASquared += Math.Pow(a[i], 2);
sigmaBSquared += Math.Pow(b[i], 2);
}
return((sigmaATimesB - (sigmaA * sigmaB) / n) /
(Math.Sqrt(sigmaASquared - Math.Pow(sigmaA, 2) / n) *
Math.Sqrt(sigmaBSquared - Math.Pow(sigmaB, 2) / n)));
}
public static double CosineSimilarity(GenericVector a, GenericVector b)
{
if (a.Dimensions != b.Dimensions)
{
throw new Exception("Distance can't be computed of vectors with different dimensions");
}
var sigmaATimesB = 0.0;
var lengthA = 0.0;
var lengthB = 0.0;
for (var i = 0; i < a.Dimensions; i++)
{
var A = a[i];
var B = b[i];
if (float.IsNaN(A))
{
A = 0;
}
if (float.IsNaN(B))
{
B = 0;
}
sigmaATimesB += A * B;
lengthA += Math.Pow(A, 2);
lengthB += Math.Pow(B, 2);
}
return(sigmaATimesB / (Math.Sqrt(lengthA) * Math.Sqrt(lengthB)));
}
private static bool HasAdditionalItems(GenericVector potentialNeighbour, GenericVector target)
{
for (int i = 0; i < target.Dimensions; i++)
{
if (float.IsNaN(target[i]) && !float.IsNaN(potentialNeighbour[i]))
{
return(true);
}
}
return(false);
}
public static double ManhattanDistanceSimilarity(GenericVector a, GenericVector b)
{
if (a.Dimensions != b.Dimensions)
{
throw new Exception("Distance can't be computed of vectors with different dimensions");
}
var sigmaAb = 0.0;
for (var i = 0; i < a.Dimensions; i++)
{
if (!float.IsNaN(a[i]) && !float.IsNaN(b[i]))
{
sigmaAb += Math.Abs(a[i] - b[i]);
}
}
return(1 / (1 + sigmaAb));
}
public static Dictionary <int, double> GetNeighbours(Matrix <float> points, int targetId, int k,
double treshold, Func <GenericVector, GenericVector, double> similarity)
{
var lowest = treshold;
var neighbours = new Dictionary <int, double>();
var target = new GenericVector(points[targetId]);
foreach (var point in points)
{
// Console.WriteLine($"point: {point.Key} with target {targetId}");
if (point.Key == targetId)
{
continue;
}
var vector = new GenericVector(point.Value);
var similar = similarity(vector, target);
if (!(similar > lowest && HasAdditionalItems(vector, target)))
{
continue;
}
if (neighbours.Count >= k)
{
var smallest = Min(neighbours);
if (similar > smallest.Value)
{
neighbours.Remove(smallest.Key);
neighbours.Add(point.Key, similar);
}
lowest = Min(neighbours).Value;
continue;
}
neighbours.Add(point.Key, similar);
}
return(neighbours);
}
