public IEnumerable<ICluster> CreateClusters(IEnumerable<IClusterable> elements, uint clusterCount)
{
if (int.MaxValue < clusterCount)
{
throw new ArgumentOutOfRangeException(nameof(clusterCount));
}
if (clusterCount < 1)
{
return Enumerable.Empty<ICluster>();
}
if (clusterCount == 1)
{
var cluster = new SimpleCluster();
cluster.AddAll(elements);
return new List<ICluster> { cluster };
}
var elementsAsList = elements as IList<IClusterable>;
if (null == elementsAsList)
{
elementsAsList = elements.ToList();
}
int clusterCountAsInt = (int)clusterCount;
if (elementsAsList.Count < clusterCountAsInt)
{
return Enumerable.Empty<ICluster>();
}
var clusters = CreateRandomClusters(elementsAsList, clusterCountAsInt);
AssignElementsToClusters(elementsAsList, clusters);
var maxIterationCount = 1E3;
for (var iteration = 0; iteration < maxIterationCount; iteration++)
{
if (UpdateClustersCenter(clusters))
{
break;
}
foreach (var cluster in clusters)
{
cluster.RemoveAll();
}
AssignElementsToClusters(elementsAsList, clusters);
}
return clusters;
}
/// <summary>
/// Creates random clusters.
/// Each cluster contains no elements and uses one element as the center of the cluster.
/// </summary>
/// <param name="elements">The elements of all clusters.</param>
/// <param name="clusterCount">The number of clusters.</param>
/// <returns>Newly created random clusters having only a center.</returns>
private IEnumerable<SimpleCluster> CreateRandomClusters(IList<IClusterable> elements, int clusterCount)
{
var clusters = new List<SimpleCluster>(clusterCount);
var centerIndices = new HashSet<int>();
var maxElementIndex = elements.Count - 1;
var maxIterationCount = 1E3;
for (var clusterIndex = 0; clusterIndex < clusterCount; clusterIndex++)
{
var newCenterFound = false;
for (var iteration = 0; !newCenterFound && iteration < maxIterationCount; iteration++)
{
var nextElementIndex = _random.Next(0, maxElementIndex);
if (!centerIndices.Contains(nextElementIndex))
{
var nextElement = elements[nextElementIndex];
var cluster = new SimpleCluster();
cluster.Center = nextElement;
clusters.Add(cluster);
centerIndices.Add(nextElementIndex);
newCenterFound = true;
break;
}
}
if (!newCenterFound)
{
throw new ArgumentException(nameof(elements));
}
}
return clusters;
}
