Github user srowen commented on a diff in the pull request:
https://github.com/apache/spark/pull/13440#discussion_r218209453
--- Diff:
mllib/src/main/scala/org/apache/spark/mllib/tree/impurity/Impurity.scala ---
@@ -52,6 +52,49 @@ trait Impurity extends Serializable {
@Since("1.0.0")
@DeveloperApi
def calculate(count: Double, sum: Double, sumSquares: Double): Double
+
+ /**
+ * :: DeveloperApi ::
+ * Compute a test-statistic p-value quality measure from left and right
split populations
+ * @param calcL impurity calculator for the left split population
+ * @param calcR impurity calculator for the right split population
+ * @return The p-value for the null hypothesis; that left and right
split populations
+ * represent the same distribution
+ * @note Unless overridden this method will fail with an exception, for
backward compatability
+ */
+ @Since("2.2.0")
+ @DeveloperApi
+ def calculate(calcL: ImpurityCalculator, calcR: ImpurityCalculator):
Double
+
+ /**
+ * :: DeveloperApi ::
+ * Determine if this impurity measure is a test-statistic measure
+ * @return True if this is a split quality measure based on a test
statistic (i.e. returns a
+ * p-value) or false otherwise.
+ * @note Unless overridden this method returns false by default, for
backward compatability
+ */
+ @Since("2.2.0")
+ @DeveloperApi
+ def isTestStatistic: Boolean
--- End diff --
Adding methods to a public trait is technically an API breaking change.
This might be considered a Developer API even though it's not labeled that way.
Still if we can avoid adding to the API here, it'd be better.
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