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Fix JaccardSimilarity.exactlyEqual throwing for small theta sketches #778

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Fix JaccardSimilarity.exactlyEqual throwing for small theta sketches #778

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9 changes: 8 additions & 1 deletion src/main/java/org/apache/datasketches/theta/JaccardSimilarity.java
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,10 @@ public static double[] jaccard(final ThetaSketch sketchA, final ThetaSketch sket
/**
* Returns true if the two given sketches have exactly the same hash values and the same
* theta values. Thus, they are equivalent.
*
* <p>Note: For very large pairs of sketches, where the configured nominal entries of the sketches
* are 2^26, this method may return false even if the two sketches are equal.
*
* @param sketchA the given sketch A
* @param sketchB the given sketch B
* @return true if the two given sketches have exactly the same hash values and the same
Expand All @@ -116,8 +120,11 @@ public static boolean exactlyEqual(final ThetaSketch sketchA, final ThetaSketch
final int countB = sketchB.getRetainedEntries(true);

//Create the ThetaUnion
final int minK = 1 << ThetaUtil.MIN_LG_NOM_LONGS;
final int maxK = 1 << ThetaUtil.MAX_LG_NOM_LONGS;
final int newK = max(min(ceilingPowerOf2(countA + countB), maxK), minK);
final ThetaUnion union =
ThetaSetOperation.builder().setNominalEntries(ceilingPowerOf2(countA + countB)).buildUnion();
ThetaSetOperation.builder().setNominalEntries(newK).buildUnion();
union.union(sketchA);
union.union(sketchB);
final ThetaSketch unionAB = union.getResult();
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11 changes: 11 additions & 0 deletions src/test/java/org/apache/datasketches/theta/JaccardSimilarityTest.java
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Expand Up @@ -233,6 +233,17 @@ public void checkMinK() {
println(result[0] + ", " + result[1] + ", " + result[2]);
}

@Test
public void checkMinKExactlyEqual() {
UpdatableThetaSketch skA = UpdatableThetaSketch.builder().build(); //4096
UpdatableThetaSketch skB = UpdatableThetaSketch.builder().build(); //4096
skA.update(1);
skB.update(1);
assertTrue(exactlyEqual(skA, skB));
skB.update(2);
assertFalse(exactlyEqual(skA, skB));
}

@Test
public void printlnTest() {
println("PRINTING: "+this.getClass().getName());
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