smile.math.distance.SparseEuclideanDistance Maven / Gradle / Ivy
/******************************************************************************
* Confidential Proprietary *
* (c) Copyright Haifeng Li 2011, All Rights Reserved *
******************************************************************************/
package smile.math.distance;
import java.util.Iterator;
import smile.math.SparseArray;
/**
* Euclidean distance. Use getInstance() to get the standard unweighted
* Euclidean distance. Or create an instance with a specified
* weight vector. For float or double arrays, missing values (i.e. NaN)
* are also handled. Also support sparse arrays of which zeros are excluded
* to save space.
*
* @author Haifeng Li
*/
public class SparseEuclideanDistance implements Metric {
/**
* The weights used in weighted distance.
*/
private double[] weight = null;
/**
* Constructor. Standard (unweighted) Euclidean distance.
*/
public SparseEuclideanDistance() {
}
/**
* Constructor with a given weight vector.
*
* @param weight the weight vector.
*/
public SparseEuclideanDistance(double[] weight) {
for (int i = 0; i < weight.length; i++) {
if (weight[i] < 0)
throw new IllegalArgumentException(String.format("Weight has to be nonnegative: %f", weight[i]));
}
this.weight = weight;
}
@Override
public String toString() {
if (weight != null)
return "weighted Euclidean distance";
else
return "Euclidean distance";
}
@Override
public double d(SparseArray x, SparseArray y) {
if (x.isEmpty())
throw new IllegalArgumentException("List x is empty.");
if (y.isEmpty())
throw new IllegalArgumentException("List y is empty.");
Iterator iterX = x.iterator();
Iterator iterY = y.iterator();
SparseArray.Entry a = iterX.hasNext() ? iterX.next() : null;
SparseArray.Entry b = iterY.hasNext() ? iterY.next() : null;
double dist = 0.0;
if (weight == null) {
while (a != null && b != null) {
if (a.i < b.i) {
double d = a.x;
dist += d * d;
a = iterX.hasNext() ? iterX.next() : null;
} else if (a.i > b.i) {
double d = b.x;
dist += d * d;
b = iterY.hasNext() ? iterY.next() : null;
} else {
double d = a.x - b.x;
dist += d * d;
a = iterX.hasNext() ? iterX.next() : null;
b = iterY.hasNext() ? iterY.next() : null;
}
}
while (a != null) {
double d = a.x;
dist += d * d;
a = iterX.hasNext() ? iterX.next() : null;
}
while (b != null) {
double d = b.x;
dist += d * d;
b = iterY.hasNext() ? iterY.next() : null;
}
} else {
while (a != null && b != null) {
if (a.i < b.i) {
double d = a.x;
dist += weight[a.i] * d * d;
a = iterX.hasNext() ? iterX.next() : null;
} else if (a.i > b.i) {
double d = b.x;
dist += weight[b.i] * d * d;
b = iterY.hasNext() ? iterY.next() : null;
} else {
double d = a.x - b.x;
dist += weight[a.i] * d * d;
a = iterX.hasNext() ? iterX.next() : null;
b = iterY.hasNext() ? iterY.next() : null;
}
}
while (a != null) {
double d = a.x;
dist += weight[a.i] * d * d;
a = iterX.hasNext() ? iterX.next() : null;
}
while (b != null) {
double d = b.x;
dist += weight[b.i] * d * d;
b = iterY.hasNext() ? iterY.next() : null;
}
}
return Math.sqrt(dist);
}
}