[jvm-packages] bring back camel case variants of parameters (#10845)

jvm-packages/xgboost4j-spark/src/main/scala/ml/dmlc/xgboost4j/scala/spark/params/ParamMapConversion.scala

@@ -18,6 +18,7 @@ package ml.dmlc.xgboost4j.scala.spark.params
 
 import scala.collection.mutable
 
+import com.google.common.base.CaseFormat
 import org.apache.spark.ml.param._
 
 private[spark] trait ParamMapConversion extends NonXGBoostParams {
@@ -28,20 +29,23 @@ private[spark] trait ParamMapConversion extends NonXGBoostParams {
    * @param xgboostParams XGBoost style parameters
    */
   def xgboost2SparkParams(xgboostParams: Map[String, Any]): Unit = {
-    for ((name, paramValue) <- xgboostParams) {
+    for ((paramName, paramValue) <- xgboostParams) {
-      params.find(_.name == name).foreach {
+      val lowerCamelName = CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.LOWER_CAMEL, paramName)
-        case _: DoubleParam =>
+      val lowerName = CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, paramName)
-          set(name, paramValue.toString.toDouble)
+      val qualifiedNames = mutable.Set(paramName, lowerName, lowerCamelName)
-        case _: BooleanParam =>
+      params.find(p => qualifiedNames.contains(p.name)) foreach {
-          set(name, paramValue.toString.toBoolean)
+        case p: DoubleParam =>
-        case _: IntParam =>
+          set(p.name, paramValue.toString.toDouble)
-          set(name, paramValue.toString.toInt)
+        case p: BooleanParam =>
-        case _: FloatParam =>
+          set(p.name, paramValue.toString.toBoolean)
-          set(name, paramValue.toString.toFloat)
+        case p: IntParam =>
-        case _: LongParam =>
+          set(p.name, paramValue.toString.toInt)
-          set(name, paramValue.toString.toLong)
+        case p: FloatParam =>
-        case _: Param[_] =>
+          set(p.name, paramValue.toString.toFloat)
-          set(name, paramValue)
+        case p: LongParam =>
+          set(p.name, paramValue.toString.toLong)
+        case p: Param[_] =>
+          set(p.name, paramValue)
       }
     }
   }
@@ -49,7 +53,7 @@ private[spark] trait ParamMapConversion extends NonXGBoostParams {
   /**
    * Convert the user-supplied parameters to the XGBoost parameters.
    *
-   * Note that this also contains jvm-specific parameters.
+   * Note that this doesn't contain jvm-specific parameters.
    */
   def getXGBoostParams: Map[String, Any] = {
     val xgboostParams = new mutable.HashMap[String, Any]()

jvm-packages/xgboost4j-spark/src/test/scala/ml/dmlc/xgboost4j/scala/spark/XGBoostEstimatorSuite.scala

@@ -69,6 +69,48 @@ class XGBoostEstimatorSuite extends AnyFunSuite with PerTest with TmpFolderPerSu
     assert(model.getContribPredictionCol === "contrib")
   }
 
+  test("camel case parameters") {
+    val xgbParams: Map[String, Any] = Map(
+      "max_depth" -> 5,
+      "featuresCol" -> "abc",
+      "num_workers" -> 2,
+      "numRound" -> 11
+    )
+    val estimator = new XGBoostClassifier(xgbParams)
+    assert(estimator.getFeaturesCol === "abc")
+    assert(estimator.getNumWorkers === 2)
+    assert(estimator.getNumRound === 11)
+    assert(estimator.getMaxDepth === 5)
+
+    val xgbParams1: Map[String, Any] = Map(
+      "maxDepth" -> 5,
+      "features_col" -> "abc",
+      "numWorkers" -> 2,
+      "num_round" -> 11
+    )
+    val estimator1 = new XGBoostClassifier(xgbParams1)
+    assert(estimator1.getFeaturesCol === "abc")
+    assert(estimator1.getNumWorkers === 2)
+    assert(estimator1.getNumRound === 11)
+    assert(estimator1.getMaxDepth === 5)
+  }
+
+  test("get xgboost parameters") {
+    val params: Map[String, Any] = Map(
+      "max_depth" -> 5,
+      "featuresCol" -> "abc",
+      "label" -> "class",
+      "num_workers" -> 2,
+      "tree_method" -> "hist",
+      "numRound" -> 11,
+      "not_exist_parameters" -> "hello"
+    )
+    val estimator = new XGBoostClassifier(params)
+    val xgbParams = estimator.getXGBoostParams
+    assert(xgbParams.size === 2)
+    assert(xgbParams.contains("max_depth") && xgbParams.contains("tree_method"))
+  }
+
   test("nthread") {
     val classifier = new XGBoostClassifier().setNthread(100)