Package org.apache.datasketches.theta
Class JaccardSimilarity
 java.lang.Object

 org.apache.datasketches.theta.JaccardSimilarity

public final class JaccardSimilarity extends Object
Jaccard similarity of two Theta Sketches. Author:
 Lee Rhodes


Constructor Summary
Constructors Constructor Description JaccardSimilarity()

Method Summary
All Methods Static Methods Concrete Methods Modifier and Type Method Description static boolean
dissimilarityTest(Sketch measured, Sketch expected, double threshold)
Tests dissimilarity of a measured Sketch against an expected Sketch.static boolean
exactlyEqual(Sketch sketchA, Sketch sketchB)
Returns true if the two given sketches have exactly the same hash values and the same theta values.static double[]
jaccard(Sketch sketchA, Sketch sketchB)
Computes the Jaccard similarity index with upper and lower bounds.static boolean
similarityTest(Sketch measured, Sketch expected, double threshold)
Tests similarity of a measured Sketch against an expected Sketch.



Method Detail

jaccard
public static double[] jaccard(Sketch sketchA, Sketch sketchB)
Computes the Jaccard similarity index with upper and lower bounds. The Jaccard similarity index J(A,B) = (A ^ B)/(A U B) is used to measure how similar the two sketches are to each other. If J = 1.0, the sketches are considered equal. If J = 0, the two sketches are distinct from each other. A Jaccard of .95 means the overlap between the two populations is 95% of the union of the two populations.Note: For very large pairs of sketches, where the configured nominal entries of the sketches are 2^25 or 2^26, this method may produce unpredictable results.
 Parameters:
sketchA
 given sketch AsketchB
 given sketch B Returns:
 a double array {LowerBound, Estimate, UpperBound} of the Jaccard index. The Upper and Lower bounds are for a confidence interval of 95.4% or +/ 2 standard deviations.

exactlyEqual
public static boolean exactlyEqual(Sketch sketchA, Sketch sketchB)
Returns true if the two given sketches have exactly the same hash values and the same theta values. Thus, they are equivalent. Parameters:
sketchA
 the given sketch AsketchB
 the given sketch B Returns:
 true if the two given sketches have exactly the same hash values and the same theta values.

similarityTest
public static boolean similarityTest(Sketch measured, Sketch expected, double threshold)
Tests similarity of a measured Sketch against an expected Sketch. Computes the lower bound of the Jaccard index J_{LB} of the measured and expected sketches. if J_{LB} ≥ threshold, then the sketches are considered to be similar with a confidence of 97.7%. Parameters:
measured
 the sketch to be testedexpected
 the reference sketch that is considered to be correct.threshold
 a real value between zero and one. Returns:
 if true, the similarity of the two sketches is greater than the given threshold with at least 97.7% confidence.

dissimilarityTest
public static boolean dissimilarityTest(Sketch measured, Sketch expected, double threshold)
Tests dissimilarity of a measured Sketch against an expected Sketch. Computes the upper bound of the Jaccard index J_{UB} of the measured and expected sketches. if J_{UB} ≤ threshold, then the sketches are considered to be dissimilar with a confidence of 97.7%. Parameters:
measured
 the sketch to be testedexpected
 the reference sketch that is considered to be correct.threshold
 a real value between zero and one. Returns:
 if true, the dissimilarity of the two sketches is greater than the given threshold with at least 97.7% confidence.

