Scala and Spark - Logistic Regression - NullPointerException

Question

Hellow everyone!

I have a problem with my scala and spark code. I am trying to implement a logistic regreesion model. For this I had to implement two UDF functions to collect my features. The problem is that every time when I try to call dataframe.show() function, I get an error:

I thought tha maybe I had null values on my dataframe and I tried to call dataframe.na.drop() in order to eliminate likely null values.

The poblem stil exists an it says that faild to execute user defined function(anonfun$3: (array, array) => int).

Here is my hole code:

val sc = spark.sparkContext

val data = sc.textFile("resources/data/training_set.txt").map(line =>{
  val fields = line.split(" ")
  (fields(0),fields(1), fields(2).toInt)
})
import spark.implicits._
val trainingDF = data.toDF("srcId","dstId", "label")
val infoRDD = spark.read.option("header","false").option("inferSchema","true").format("csv").load("resources/data/node_information.csv")

val infoDF = infoRDD.toDF("srcId","year","title","authors","jurnal","abstract")

println("Showing linksDF sample...")
trainingDF.show(5)
println("Rows of linksDF: ",trainingDF.count())

println("Showing infoDF sample...")
infoDF.show(2)
println("Rows of infoDF: ",infoDF.count())

println("Joining linksDF and infoDF...")
var joinedDF = trainingDF.as("a").join(infoDF.as("b"),$"a.srcId" === $"b.srcId")

println(joinedDF.count())

joinedDF = joinedDF.select($"a.srcId",$"a.dstId",$"a.label",$"b.year",$"b.title",$"b.authors",$"b.jurnal",$"b.abstract")

println("Renameming joinedDF...")
joinedDF = joinedDF
  .withColumnRenamed("srcId","id_from")
  .withColumnRenamed("dstId","id_to")
  .withColumnRenamed("year","year_from")
  .withColumnRenamed("title","title_from")
  .withColumnRenamed("authors","authors_from")
  .withColumnRenamed("jurnal","jurnal_from")
  .withColumnRenamed("abstract","abstract_from")

var infoDfRenamed = joinedDF
  .withColumnRenamed("id_from","id_from")
  .withColumnRenamed("id_to","id_to")
  .withColumnRenamed("year_from","year_to")
  .withColumnRenamed("title_from","title_to")
  .withColumnRenamed("authors_from","authors_to")
  .withColumnRenamed("jurnal_from","jurnal_to")
  .withColumnRenamed("abstract_from","abstract_to").select("id_to","year_to","title_to","authors_to","jurnal_to","jurnal_to")

var finalDF = joinedDF.as(("a")).join(infoDF.as("b"),$"a.id_to" === $"b.srcId")

finalDF = finalDF
  .withColumnRenamed("year","year_to")
  .withColumnRenamed("title","title_to")
  .withColumnRenamed("authors","authors_to")
  .withColumnRenamed("jurnal","jurnal_to")
  .withColumnRenamed("abstract","abstract_to")

println("Dropping unused columns from joinedDF...")
finalDF = finalDF.drop("srcId")


println("Spliting title_from column into words...")
finalDF = finalDF.withColumn("title_from_words", functions.split(col("title_from"), "\\s+"))
println("Spliting title_to column into words...")
finalDF = finalDF.withColumn("title_to_words", functions.split(col("title_to"), "\\s+"))

println("Spliting authors_from column into words...")
finalDF = finalDF.withColumn("authors_from_words", functions.split(col("authors_from"), "\\s+"))
println("Spliting authors_to column into words...")
finalDF = finalDF.withColumn("authors_to_words", functions.split(col("authors_to"), "\\s+"))

println("Removing stopwords from title_from column...")
val remover = new StopWordsRemover().setInputCol("title_from_words").setOutputCol("title_from_words_f")
finalDF = remover.transform(finalDF)

println("Removing stopwords from title_to column...")
val remover2 = new StopWordsRemover().setInputCol("title_to_words").setOutputCol("title_to_words_f")
finalDF = remover2.transform(finalDF)

println("Removing stopwords from authors_from column...")
val remover3 = new StopWordsRemover().setInputCol("authors_from_words").setOutputCol("authors_from_words_f")
finalDF = remover3.transform(finalDF)

println("Removing stopwords from authors_to column...")
val remover4 = new StopWordsRemover().setInputCol("authors_to_words").setOutputCol("authors_to_words_f")
finalDF = remover4.transform(finalDF)

finalDF.count() 

val udf_title_overlap=udf(findNumberCommonWordsTitle(_:Seq[String],_:Seq[String]))
val udf_authors_overlap = udf(findNumberCommonAuthors(_:Seq[String], _:Seq[String]))

println("Getting the number of common words between title_from and title_to columns using UDF function...")
finalDF = finalDF.withColumn("titles_intersection",udf_title_overlap(finalDF("title_from_words"),finalDF("title_to_words")))

println("Getting the number of common words between authors_from and authors_to columns using UDF function...")
finalDF = finalDF.withColumn("authors_intersection",udf_authors_overlap(finalDF("aut 
hors_from_words"),finalDF("authors_to_words")))

finalDF.count()

finalDF = finalDF.withColumn("time_dist",abs($"year_from" - 
$"year_to"))

println("Show schema of finalDF:\n")
finalDF.printSchema()

println("Dropping unused columns from finalDF...\n")
val finalCollsDF = finalDF.select("label","titles_intersection", 
"authors_intersection", "time_dist")

println("Printing schema for finalDF...\n")
finalCollsDF.printSchema()

println("Creating features coll from finalDF using 
VectorAssembler...\n")
val assembler = new VectorAssembler()
  .setInputCols(Array("titles_intersection", "authors_intersection", 
"time_dist"))
  .setOutputCol("features")

val output = assembler.transform(finalCollsDF)

println("Printing final schema before trainning...\n")
output.printSchema()
output.na.drop()

println("Splitting dataset into trainingData and testData...\n")
val Array(trainingData, testData) = output.randomSplit(Array(0.6, 
0.4))

val lr = new LogisticRegression()
  .setFeaturesCol("features")
  .setLabelCol("label")
  .setPredictionCol("prediction")
  .setRawPredictionCol("prediction_raw")
  .setMaxIter(10)

val lr_model = lr.fit(trainingData)

val lr_results = lr_model.transform(testData)

val evaluator = new BinaryClassificationEvaluator()
  .setRawPredictionCol("prediction_raw")
  .setLabelCol("label")
  .setMetricName("areaUnderPR")

println("RESULTS FOR LOGISTIC REGRESSION:")
println(evaluator.evaluate(lr_results))

}

The two UDF functions which I am using are the following:

 def findNumberCommonWordsTitle(title_from:Seq[String], 
   title_to:Seq[String]) ={
   val intersection = title_from.intersect(title_to)
   intersection.length
    }

  def findNumberCommonAuthors(author_from:Seq[String], 
   author_to:Seq[String])={
  val intersection = author_from.intersect(author_to)
   intersection.length
  }

I had searched for null values manualy using a foreach statement but it did not worked too. How can I fix this problem. Maybe I is another problem which I can not find.

Thanks

Answer 1

Spark allow values to be null in dataframes, so calling the UDF on columns of that dataframe may result in NullPointerExceptions if for example one or both arrays are null .

You should check in your UDF for null values and handle these accordingly, or make sure the column in the dataframe may not be null and set null values to empty arrays.

 def findNumberCommonAuthors(author_from:Seq[String], author_to:Seq[String])={
   if(author_from == null || author_to == null) 0
   else author_from.intersect(author_to).length
  }