/// <summary>
/// Trains the centroids.
/// </summary>
public void Train(InstanceRepresentation set)
{
var instances = set.Instances.ToArray();
// Initializing the centroids:
if (_usePlusPlusInit)
{
_centroids = PlusPlusInitializer.InitializeCentroids(K, instances, _random);
}
else
{
_centroids = Instances.ConvertToArray(instances.SampleNoReplacement(K, _random));
}
_isInitialized = true;
FeaturesCount = set.FeauturesCount;
for (var i = 0; i < _iterationsCount; i++)
{
var miniBatch = instances.SampleReplacement(_minibatchSize, _random);
MiniBatchUpdate(miniBatch, set.IsSparseDataset);
}
}
public void MiniBatchUpdate(IInstance[] miniBatch, bool isSparseMiniBatch)
{
var minibathSize = miniBatch.Length;
if (!_isInitialized)
{
// Initializing the centroids:
if (_usePlusPlusInit)
{
_centroids = PlusPlusInitializer.InitializeCentroids(K, miniBatch, _random);
}
else
{
_centroids = Instances.ConvertToArray(
miniBatch.SampleReplacement(FeaturesCount, _random));
}
_isInitialized = true;
}
var nearestClusters = new int[_minibatchSize];
var perCenterCount = new int[_centroids.Length];
for (var j = 0; j < minibathSize; j++)
{
nearestClusters[j] = Instances.MinEucDistanceIndex(miniBatch[j], _centroids);
}
// If the dataset is not sparse we perform the non sparse cluster computation.
if (!isSparseMiniBatch)
{
for (var j = 0; j < minibathSize; j++)
{
perCenterCount[nearestClusters[j]] += 1;
var learningRate = 1.0 / perCenterCount[nearestClusters[j]];
for (var k = 0; k < FeaturesCount; k++)
{
var c = _centroids[nearestClusters[j], k];
_centroids[nearestClusters[j], k] = (float)((1.0 - learningRate) * c + miniBatch[j].GetValue(k) * learningRate);
}
}
}
else // If the dataset is sparse we perform the sparse clustering version.
{
for (var j = 0; j < minibathSize; j++)
{
var current = _centroids.L1Norm(nearestClusters[j], FeaturesCount);
if (current <= Epsilon + Lambda)
{
break;
}
var upper = _centroids.Max(nearestClusters[j], FeaturesCount);
var lower = 0.0;
var theta = 0.0;
while (current < Lambda * (Epsilon + 1) || current < Lambda)
{
theta = (upper + lower) / 2.0; // Get L1 value
current = 0.0;
for (var k = 0; k < FeaturesCount; k++)
{
current += Math.Max(0, Math.Abs(_centroids[nearestClusters[j], k]) - theta);
if (current <= Lambda)
{
upper = theta;
}
else
{
lower = theta;
}
}
}
for (var k = 0; k < FeaturesCount; k++)
{
var c = _centroids[nearestClusters[j], k];
_centroids[nearestClusters[j], k] = (float)(Math.Sign(c) * Math.Max(0, Math.Abs(c) - theta));
}
}
}
}