PhillHenry commented on a change in pull request #31535:
URL: https://github.com/apache/spark/pull/31535#discussion_r575104665



##########
File path: 
mllib/src/main/scala/org/apache/spark/ml/tuning/ParamRandomBuilder.scala
##########
@@ -0,0 +1,145 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ml.tuning
+
+import org.apache.spark.annotation.Since
+import org.apache.spark.ml.param._
+
+case class Limits[T: Numeric](x: T, y: T)
+
+abstract class RandomT[T: Numeric] {
+  def randomT(): T
+  def randomTLog(n: Int): T
+}
+
+abstract class Generator[T: Numeric] {
+  def apply(lim: Limits[T]): RandomT[T]
+}
+
+object RandomRanges {
+
+  val rnd = new scala.util.Random
+
+  private[tuning] def randomBigInt0To(x: BigInt): BigInt = {
+    var randVal = BigInt(x.bitLength, rnd)
+    while (randVal > x) {
+      randVal = BigInt(x.bitLength, rnd)
+    }
+    randVal
+  }
+
+  def bigIntBetween(lower: BigInt, upper: BigInt): BigInt = {
+    val diff: BigInt = upper - lower
+    randomBigInt0To(diff) + lower
+  }
+
+  private def randomBigDecimalBetween(lower: BigDecimal, upper: BigDecimal): 
BigDecimal = {
+    val zeroCenteredRnd: BigDecimal = BigDecimal(rnd.nextDouble() - 0.5)
+    val range: BigDecimal = upper - lower
+    val halfWay: BigDecimal = lower + range / 2
+    (zeroCenteredRnd * range) + halfWay
+  }
+
+  implicit object DoubleGenerator extends Generator[Double] {
+    def apply(limits: Limits[Double]): RandomT[Double] = new RandomT[Double] {
+      import limits._
+      val lower: Double = math.min(x, y)
+      val upper: Double = math.max(x, y)
+
+      override def randomTLog(n: Int): Double =
+        RandomRanges.randomLog(lower, upper, n)
+
+      override def randomT(): Double =
+        randomBigDecimalBetween(BigDecimal(lower), 
BigDecimal(upper)).doubleValue
+    }
+  }
+
+  implicit object FloatGenerator extends Generator[Float] {
+    def apply(limits: Limits[Float]): RandomT[Float] = new RandomT[Float] {
+      import limits._
+      val lower: Float = math.min(x, y)
+      val upper: Float = math.max(x, y)
+
+      override def randomTLog(n: Int): Float =
+        RandomRanges.randomLog(lower, upper, n).toFloat
+
+      override def randomT(): Float =
+        randomBigDecimalBetween(BigDecimal(lower), 
BigDecimal(upper)).floatValue
+    }
+  }
+
+  implicit object IntGenerator extends Generator[Int] {
+    def apply(limits: Limits[Int]): RandomT[Int] = new RandomT[Int] {
+      import limits._
+      val lower: Int = math.min(x, y)
+      val upper: Int = math.max(x, y)
+
+      override def randomTLog(n: Int): Int =
+        RandomRanges.randomLog(lower, upper, n).toInt
+
+      override def randomT(): Int =
+        bigIntBetween(BigInt(lower), BigInt(upper)).intValue
+    }
+  }
+
+  implicit object LongGenerator extends Generator[Long] {

Review comment:
       I included it for completeness. I can remove it if you like.

##########
File path: 
mllib/src/main/scala/org/apache/spark/ml/tuning/ParamRandomBuilder.scala
##########
@@ -0,0 +1,145 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.ml.tuning
+
+import org.apache.spark.annotation.Since
+import org.apache.spark.ml.param._
+
+case class Limits[T: Numeric](x: T, y: T)
+
+abstract class RandomT[T: Numeric] {
+  def randomT(): T
+  def randomTLog(n: Int): T
+}
+
+abstract class Generator[T: Numeric] {
+  def apply(lim: Limits[T]): RandomT[T]
+}
+
+object RandomRanges {
+
+  val rnd = new scala.util.Random
+
+  private[tuning] def randomBigInt0To(x: BigInt): BigInt = {
+    var randVal = BigInt(x.bitLength, rnd)
+    while (randVal > x) {
+      randVal = BigInt(x.bitLength, rnd)
+    }
+    randVal
+  }
+
+  def bigIntBetween(lower: BigInt, upper: BigInt): BigInt = {
+    val diff: BigInt = upper - lower
+    randomBigInt0To(diff) + lower
+  }
+
+  private def randomBigDecimalBetween(lower: BigDecimal, upper: BigDecimal): 
BigDecimal = {
+    val zeroCenteredRnd: BigDecimal = BigDecimal(rnd.nextDouble() - 0.5)
+    val range: BigDecimal = upper - lower
+    val halfWay: BigDecimal = lower + range / 2
+    (zeroCenteredRnd * range) + halfWay
+  }
+
+  implicit object DoubleGenerator extends Generator[Double] {
+    def apply(limits: Limits[Double]): RandomT[Double] = new RandomT[Double] {
+      import limits._
+      val lower: Double = math.min(x, y)
+      val upper: Double = math.max(x, y)
+
+      override def randomTLog(n: Int): Double =
+        RandomRanges.randomLog(lower, upper, n)
+
+      override def randomT(): Double =
+        randomBigDecimalBetween(BigDecimal(lower), 
BigDecimal(upper)).doubleValue
+    }
+  }
+
+  implicit object FloatGenerator extends Generator[Float] {
+    def apply(limits: Limits[Float]): RandomT[Float] = new RandomT[Float] {
+      import limits._
+      val lower: Float = math.min(x, y)
+      val upper: Float = math.max(x, y)
+
+      override def randomTLog(n: Int): Float =
+        RandomRanges.randomLog(lower, upper, n).toFloat
+
+      override def randomT(): Float =
+        randomBigDecimalBetween(BigDecimal(lower), 
BigDecimal(upper)).floatValue
+    }
+  }
+
+  implicit object IntGenerator extends Generator[Int] {
+    def apply(limits: Limits[Int]): RandomT[Int] = new RandomT[Int] {
+      import limits._
+      val lower: Int = math.min(x, y)
+      val upper: Int = math.max(x, y)
+
+      override def randomTLog(n: Int): Int =
+        RandomRanges.randomLog(lower, upper, n).toInt
+
+      override def randomT(): Int =
+        bigIntBetween(BigInt(lower), BigInt(upper)).intValue
+    }
+  }
+
+  implicit object LongGenerator extends Generator[Long] {
+    def apply(limits: Limits[Long]): RandomT[Long] = new RandomT[Long] {
+      import limits._
+      val lower: Long = math.min(x, y)
+      val upper: Long = math.max(x, y)
+
+      override def randomTLog(n: Int): Long =
+        RandomRanges.randomLog(lower, upper, n).toLong
+
+      override def randomT(): Long =
+        bigIntBetween(BigInt(lower), BigInt(upper)).longValue
+    }
+  }
+
+  def logN(x: Double, base: Int): Double = math.log(x) / math.log(base)
+
+  def randomLog(lower: Double, upper: Double, n: Int): Double = {
+    val logLower: Double = logN(lower, n)
+    val logUpper: Double = logN(upper, n)
+    val logLimits: Limits[Double] = Limits(logLower, logUpper)
+    val rndLogged: RandomT[Double] = RandomRanges(logLimits)
+    math.pow(n, rndLogged.randomT())
+  }
+
+  def apply[T: Generator](lim: Limits[T])(implicit t: Generator[T]): 
RandomT[T] = t(lim)
+
+}
+
+/**
+ * "For any distribution over a sample space with a finite maximum, the 
maximum of 60 random
+ * observations lies within the top 5% of the true maximum, with 95% 
probability"
+ * - Evaluating Machine Learning Models by Alice Zheng
+ * 
https://www.oreilly.com/library/view/evaluating-machine-learning/9781492048756/ch04.html
+ *
+ * Note: if you want more sophisticated hyperparameter tuning, consider Python 
libraries
+ * such as Hyperopt.
+ */
+@Since("3.1.0")

Review comment:
       Done.




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