/**
* Computes a minimum aggregation on the distance of a data point to cluster centers.
*
* <p>Output Format: 0: centerID 1: pointVector 2: constant(1) (to enable combinable average
* computation in the following reducer)
*/
@Override
public void reduce(Iterator<PactRecord> pointsWithDistance, Collector<PactRecord> out) {
double nearestDistance = Double.MAX_VALUE;
int nearestClusterId = 0;
// check all cluster centers
while (pointsWithDistance.hasNext()) {
PactRecord res = pointsWithDistance.next();
double distance = res.getField(3, PactDouble.class).getValue();
// compare distances
if (distance < nearestDistance) {
// if distance is smaller than smallest till now, update nearest cluster
nearestDistance = distance;
nearestClusterId = res.getField(2, PactInteger.class).getValue();
res.getFieldInto(1, this.position);
}
}
// emit a new record with the center id and the data point. add a one to ease the
// implementation of the average function with a combiner
this.centerId.setValue(nearestClusterId);
this.result.setField(0, this.centerId);
this.result.setField(1, this.position);
this.result.setField(2, this.one);
out.collect(this.result);
}
/* (non-Javadoc)
* @see eu.stratosphere.pact.runtime.plugable.TypeAccessors#setReferenceForEquality(java.lang.Object)
*/
@Override
public void setReference(PactRecord toCompare) {
for (int i = 0; i < this.keyFields.length; i++) {
if (!toCompare.getFieldInto(this.keyFields[i], this.keyHolders[i])) {
throw new NullKeyFieldException(this.keyFields[i]);
}
}
}
