I'm using the MatrixFactorizationModel.predict() method and encountered the
following exception:
Name: java.util.NoSuchElementException
Message: next on empty iterator
StackTrace: scala.collection.Iterator$$anon$2.next(Iterator.scala:39)
scala.collection.Iterator$$anon$2.next(Iterator.scala:37)
scala.collection.IndexedSeqLike$Elements.next(IndexedSeqLike.scala:64)
scala.collection.IterableLike$class.head(IterableLike.scala:91)
scala.collection.mutable.ArrayBuffer.scala$collection$IndexedSeqOptimized$$super$head(ArrayBuffer.scala:47)
scala.collection.IndexedSeqOptimized$class.head(IndexedSeqOptimized.scala:120)
scala.collection.mutable.ArrayBuffer.head(ArrayBuffer.scala:47)
org.apache.spark.mllib.recommendation.MatrixFactorizationModel.predict(MatrixFactorizationModel.scala:81)
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$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:81)
$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:83)
$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:85)
$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:87)
$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:89)
$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:91)
$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:93)
$line78.$read$$iwC$$iwC$$iwC$$iwC$$iwC.<init>(<console>:95)
$line78.$read$$iwC$$iwC$$iwC$$iwC.<init>(<console>:97)
$line78.$read$$iwC$$iwC$$iwC.<init>(<console>:99)
$line78.$read$$iwC$$iwC.<init>(<console>:101)
$line78.$read$$iwC.<init>(<console>:103)
$line78.$read.<init>(<console>:105)
$line78.$read$.<init>(<console>:109)
$line78.$read$.<clinit>(<console>)
$line78.$eval$.<init>(<console>:7)
$line78.$eval$.<clinit>(<console>)
$line78.$eval.$print(<console>)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:95)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:55)
java.lang.reflect.Method.invoke(Method.java:507)
org.apache.spark.repl.SparkIMain$ReadEvalPrint.call(SparkIMain.scala:1065)
org.apache.spark.repl.SparkIMain$Request.loadAndRun(SparkIMain.scala:1346)
org.apache.spark.repl.SparkIMain.loadAndRunReq$1(SparkIMain.scala:840)
org.apache.spark.repl.SparkIMain.interpret(SparkIMain.scala:871)
org.apache.spark.repl.SparkIMain.interpret(SparkIMain.scala:819)
com.ibm.spark.interpreter.ScalaInterpreter$$anonfun$interpretAddTask$1$$anonfun$apply$3.apply(ScalaInterpreter.scala:296)
com.ibm.spark.interpreter.ScalaInterpreter$$anonfun$interpretAddTask$1$$anonfun$apply$3.apply(ScalaInterpreter.scala:291)
com.ibm.spark.global.StreamState$.withStreams(StreamState.scala:80)
com.ibm.spark.interpreter.ScalaInterpreter$$anonfun$interpretAddTask$1.apply(ScalaInterpreter.scala:290)
com.ibm.spark.interpreter.ScalaInterpreter$$anonfun$interpretAddTask$1.apply(ScalaInterpreter.scala:290)
com.ibm.spark.utils.TaskManager$$anonfun$add$2$$anon$1.run(TaskManager.scala:123)
java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1153)
java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
java.lang.Thread.run(Thread.java:785)
This took some debugging to figure out why I received the Exception, but
when looking at the predict() implementation, I seems to assume that there
will always be features found for the provided user and product ids:
/** Predict the rating of one user for one product. */
@Since("0.8.0")
def predict(user: Int, product: Int): Double = {
val userVector = userFeatures.lookup(user).head
val productVector = productFeatures.lookup(product).head
blas.ddot(rank, userVector, 1, productVector, 1)
}
It would be helpful if a more useful exception was raised, e.g.
MissingUserFeatureException : "User ID ${user} not found in model"
MissingProductFeatureException : "Product ID ${product} not found in model"
WDYT?
