/// <summary>
/// Finds exactly the cluster closest to the cluster whose label matches color1 and the points
/// in each cluster that are closest, along with the square distance between them.
/// </summary>
/// <param name="color1">Label of the cluster whose nearest neighbor is being sought.</param>
/// <returns>A point in the cluster corresponding to color1, the closest point to it
/// from another cluster, the square distance between the points, and the label of the other cluster.
/// NOTE: ClosestPair.Color1 will equal color1.
/// </returns>
public ClosestPair FindClusterExhaustively(TLabel color1)
{
var shortest = new ClosestPair();
foreach (var p1 in Clusters.PointsInClass(color1))
{
foreach (var pc in Clusters.Points()
.Select(p => new { Point = p, Color = Clusters.GetClassLabel(p) })
.Where(pc => !color1.Equals(pc.Color)))
{
var d = p1.Measure(pc.Point);
if (d < shortest.SquareDistance)
{
shortest.SquareDistance = d;
shortest.Color1 = color1;
shortest.Point1 = p1;
shortest.Color2 = pc.Color;
shortest.Point2 = pc.Point;
}
}
}
//TODO: If there is only one cluster, the if statement above will not be triggered and shortest will
// be ill-defined and cause a Null Pointer exception in Swap.
return(shortest.Swap(color1));
}
/// <summary>
/// Finds an approximately closest pair of points (one of each color) by using the ordering found in SortedPoints.
///
/// This compares points in two of the clusters, ignoring points in all other clusters.
///
/// NOTE: This was a good idea, but yields results too poor to be used.
/// </summary>
/// <param name="color1">Label of the first cluster.</param>
/// <param name="color2">Label of the second cluster.</param>
/// <returns>The point with Color1, the point with Color2 and the square distance between them.
/// </returns>
public ClosestPair FindPairApproximately(TLabel color1, TLabel color2)
{
var shortest = new ClosestPair();
UnsignedPoint prevP = null;
TLabel prevColor = default(TLabel);
foreach (var pc in SortedPoints
.Select(p => new { Point = p, Color = Clusters.GetClassLabel(p) })
.Where(pc => pc.Color.Equals(color1) || pc.Color.Equals(color2)))
{
if (prevP != null && !prevColor.Equals(pc.Color))
{
var d = pc.Point.Measure(prevP);
if (d < shortest.SquareDistance)
{
shortest.SquareDistance = d;
shortest.Color1 = prevColor;
shortest.Point1 = prevP;
shortest.Color2 = pc.Color;
shortest.Point2 = pc.Point;
}
}
prevP = pc.Point;
prevColor = pc.Color;
}
return(shortest.Swap(color1));
}
/// <summary>
/// Approximates the closest distance between every cluster and every other cluster.
///
/// If there are currently K clusters, this will return at most K(K-1)/2 ClosestPairs, unsorted.
/// If an upper limit on the square distance is supplied, fewer may be returned.
/// </summary>
/// <param name="maxSquareDistance">If omitted, no restriction on distance is applied.
/// If supplied, no measurement of the closest distance between two colors will
/// be returned if those two colors are farther apart than this distance.
/// </param>
/// <returns>ClosestPairs for every pair of colors, unsorted.
/// If a distance is returned for colors "A" and "B", one will not be returned for colors "B" and "A",
/// since the distance is symmetric.</returns>
public IEnumerable <ClosestPair> FindAllClustersApproximately(long maxSquareDistance = long.MaxValue)
{
var colors = Clusters.ClassLabels().ToArray();
for (var i = 0; i < colors.Length; i++)
{
for (var j = i + 1; j < colors.Length; j++)
{
var closest = NearestPointFinder.FindNearestWithLabel(colors[i], colors[j]);
var shortest = new ClosestPair(closest.SearchLabel, closest.SearchPoint, closest.NearLabel, closest.NearPoint, closest.Measure);
yield return(shortest.Swap(colors[i]));
}
}
}
/// <summary>
/// Finds approximately the cluster nearest to the given cluster.
/// </summary>
/// <param name="color1">Identifies the cluster being queried.</param>
/// <returns>The closest cluster and the points from each cluster that were closest.</returns>
public ClosestPair FindClusterApproximately(TLabel color1)
{
if (EqualityComparer <TLabel> .Default.Equals(color1, default(TLabel)))
{
throw new ArgumentNullException(nameof(color1));
}
// A contiguous segment of points that are not color1 is sandwiched between
// two points that are color1, except possibly at the beginning and end of the list of SortedPoints.
// If multiple points from the same second color are found in the segment,
// only compare the nearest point in sequence to each end of the segment.
// For example, if the sequence of colors (1,2,3) for points A thru J is this:
// Points: A B C D E F G H I J
// Colors: 1 2 2 2 3 3 3 2 2 1
// We will compare the distances between A & B, A & E, G & J, and I & J,
// because they are likeliest to be the closest points to one or the other endpoints (A & J).
// Thus at most one point of each color found in the segment will be compared to the
// first point of color1, and at most one point of each color will be compared to the last
// point of color1.
var closest = this.NearestPointFinder.FindNearest(color1);
var shortest = new ClosestPair(closest.SearchLabel, closest.SearchPoint, closest.NearLabel, closest.NearPoint, closest.Measure);
return(shortest.Swap(color1));
}
