This sounds like some missing required config in engine.json. Can you share the file?
From: Anuj Kumar <[email protected]> <[email protected]> Reply: [email protected] <[email protected]> <[email protected]> Date: June 18, 2018 at 5:05:22 AM To: [email protected] <[email protected]> <[email protected]> Subject: java.util.NoSuchElementException: head of empty list when running train Getting this while running "pio train". Please help Exception in thread "main" java.util.NoSuchElementException: head of empty list at scala.collection.immutable.Nil$.head(List.scala:420) at scala.collection.immutable.Nil$.head(List.scala:417) at org.apache.mahout.math.cf.SimilarityAnalysis$.crossOccurrenceDownsampled(SimilarityAnalysis.scala:177) at com.actionml.URAlgorithm.calcAll(URAlgorithm.scala:343) at com.actionml.URAlgorithm.train(URAlgorithm.scala:295) at com.actionml.URAlgorithm.train(URAlgorithm.scala:180) at org.apache.predictionio.controller.P2LAlgorithm.trainBase(P2LAlgorithm.scala:49) at org.apache.predictionio.controller.Engine$$anonfun$18.apply(Engine.scala:690) at org.apache.predictionio.controller.Engine$$anonfun$18.apply(Engine.scala:690) at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234) at scala.collection.TraversableLike$$anonfun$map$1.apply(TraversableLike.scala:234) at scala.collection.immutable.List.foreach(List.scala:381) at scala.collection.TraversableLike$class.map(TraversableLike.scala:234) at scala.collection.immutable.List.map(List.scala:285) at org.apache.predictionio.controller.Engine$.train(Engine.scala:690) at org.apache.predictionio.controller.Engine.train(Engine.scala:176) at org.apache.predictionio.workflow.CoreWorkflow$.runTrain(CoreWorkflow.scala:67) at org.apache.predictionio.workflow.CreateWorkflow$.main(CreateWorkflow.scala:251) at org.apache.predictionio.workflow.CreateWorkflow.main(CreateWorkflow.scala) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.apache.spark.deploy.SparkSubmit$.org$apache$spark$deploy$SparkSubmit$$runMain(SparkSubmit.scala:743) at org.apache.spark.deploy.SparkSubmit$.doRunMain$1(SparkSubmit.scala:187) at org.apache.spark.deploy.SparkSubmit$.submit(SparkSubmit.scala:212) at org.apache.spark.deploy.SparkSubmit$.main(SparkSubmit.scala:126) at org.apache.spark.deploy.SparkSubmit.main(SparkSubmit.scala) -- - Best, Anuj Kumar
