[jvm-packages] Allow supression of Rabit output in Booster::train in xgboost4j (#4262)

* Make train in xgboost4j respect print params

Previously no setting in params argument of Booster::train would prevent
the Rabit.trackerPrint call. This can fill up a lot of screen space in
the case that many folds are being trained.
* Setting "silent" in this map to "true", "True", a non-zero integer, or
  a string that can be parsed to such an int will prevent printing.
* Setting "verbose_eval" to "False" or "false" will prevent printing.
* Setting "verbose_eval" to an int (or a String parseable to an int) n
  will result in printing every n steps, or no printing is n is zero.

This is to match the python behaviour described here:
https://www.kaggle.com/c/rossmann-store-sales/discussion/17499

* Fixed 'slient' typo in xgboost4j test

* private access on two methods

jvm-packages/xgboost4j/src/main/java/ml/dmlc/xgboost4j/java/XGBoost.java

@@ -228,8 +228,10 @@ public class XGBoost {
             break;
           }
         }
-        if (Rabit.getRank() == 0) {
+        if (Rabit.getRank() == 0 && shouldPrint(params, iter)) {
-          Rabit.trackerPrint(evalInfo + '\n');
+          if (shouldPrint(params, iter)){
+            Rabit.trackerPrint(evalInfo + '\n');
+          }
         }
       }
       booster.saveRabitCheckpoint();
@@ -237,6 +239,47 @@ public class XGBoost {
     return booster;
   }
 
+  private static Integer tryGetIntFromObject(Object o) {
+    if (o instanceof Integer) {
+      return (int)o;
+    } else if (o instanceof String) {
+      try {
+        return Integer.parseInt((String)o);
+      } catch (NumberFormatException e) {
+        return null;
+      }
+    } else {
+      return null;
+    }
+  }
+
+  private static boolean shouldPrint(Map<String, Object> params, int iter) {
+    Object silent = params.get("silent");
+    Integer silentInt = tryGetIntFromObject(silent);
+    if (silent != null) {
+      if (silent.equals("true") || silent.equals("True")
+              || (silentInt != null && silentInt != 0)) {
+        return false;  // "silent" will stop printing, otherwise go look at "verbose_eval"
+      }
+    }
+
+    Object verboseEval = params.get("verbose_eval");
+    Integer verboseEvalInt = tryGetIntFromObject(verboseEval);
+    if (verboseEval == null) {
+      return true; // Default to printing evalInfo
+    } else if (verboseEval.equals("false") || verboseEval.equals("False")) {
+      return false;
+    } else if (verboseEvalInt != null) {
+      if (verboseEvalInt == 0) {
+        return false;
+      } else {
+        return iter % verboseEvalInt == 0;
+      }
+    } else {
+      return true; // Don't understand the option, default to printing
+    }
+  }
+
   static boolean shouldEarlyStop(int earlyStoppingRounds, int iter, int bestIteration) {
     return iter - bestIteration >= earlyStoppingRounds;
   }

jvm-packages/xgboost4j/src/test/scala/ml/dmlc/xgboost4j/scala/ScalaBoosterImplSuite.scala

@@ -139,7 +139,7 @@ class ScalaBoosterImplSuite extends FunSuite {
 
   test("cross validation") {
     val trainMat = new DMatrix("../../demo/data/agaricus.txt.train")
-    val params = List("eta" -> "1.0", "max_depth" -> "3", "slient" -> "1", "nthread" -> "6",
+    val params = List("eta" -> "1.0", "max_depth" -> "3", "silent" -> "1", "nthread" -> "6",
       "objective" -> "binary:logistic", "gamma" -> "1.0", "eval_metric" -> "error").toMap
     val round = 2
     val nfold = 5