Splitting strings in Apache Spark using Scala

Question

I have a dataset, which contains lines in the format (tab separated):

Title<\\t>Text

Now for every word in Text, I want to c

Answer 1

The answer which proved above is not good enough. .map( line => line.split("\t") ) may cause:

org.apache.spark.SparkException: Job aborted due to stage failure: Task 0 in stage 18.0 failed 4 times, most recent failure: Lost task 0.3 in stage 18.0 (TID 1485, ip-172-31-113-181.us-west-2.compute.internal, executor 10): java.lang.RuntimeException: Error while encoding: java.lang.ArrayIndexOutOfBoundsException: 14

in case the last column is empty. the best result explained here - Split 1 column into 3 columns in spark scala

Answer 2

Another version with DataFrame API

// read into DataFrame
val viewsDF=spark.read.text("s3n://file.txt")

// Split
val splitedViewsDF = viewsDF.withColumn("col1", split($"value", "\\t").getItem(0)).withColumn("col2", split($"value", "\\s+").getItem(1)).drop($"value"))

Sample

scala> val viewsDF=spark.read.text("spark-labs/data/wiki-pageviews.txt")
viewsDF: org.apache.spark.sql.DataFrame = [value: string]

scala> viewsDF.printSchema
root
 |-- value: string (nullable = true)


scala> viewsDF.limit(5).show
+------------------+
|             value|
+------------------+
|  aa Main_Page 3 0|
|  aa Main_page 1 0|
|  aa User:Savh 1 0|
|  aa Wikipedia 1 0|
|aa.b User:Savh 1 0|
+------------------+


scala> val splitedViewsDF = viewsDF.withColumn("col1", split($"value", "\\s+").getItem(0)).withColumn("col2", split($"value", "\\s+").getItem(1)).withColumn("col3", split($"value", "\\s+").getItem(2)).drop($"value")
splitedViewsDF: org.apache.spark.sql.DataFrame = [col1: string, col2: string ... 1 more field]

scala>

scala> splitedViewsDF.printSchema
root
 |-- col1: string (nullable = true)
 |-- col2: string (nullable = true)
 |-- col3: string (nullable = true)


scala> splitedViewsDF.limit(5).show
+----+---------+----+
|col1|     col2|col3|
+----+---------+----+
|  aa|Main_Page|   3|
|  aa|Main_page|   1|
|  aa|User:Savh|   1|
|  aa|Wikipedia|   1|
|aa.b|User:Savh|   1|
+----+---------+----+


scala>

Answer 3

This is how it can be solved using the newer dataframe API. First read the data using "\t" as a delimiter:

val df = spark.read
  .option("delimiter", "\t")
  .option("header", false)
  .csv("s3n://file.txt")
  .toDF("title", "text")

Then, split the text column on space and explode to get one word per row.

val df2 = df.select($"title", explode(split($"text", " ")).as("words"))

Finally, group on the title column and count the number of words for each.

val countDf = df2.groupBy($"title").agg(count($"words"))

Answer 4

So... In spark you work using distributed data structure called RDD. They provide functionality similar to scala's collection types.

val fileRdd = sc.textFile("s3n://file.txt")
// RDD[ String ]

val splitRdd = fileRdd.map( line => line.split("\t") )
// RDD[ Array[ String ]

val yourRdd = splitRdd.flatMap( arr => {
  val title = arr( 0 )
  val text = arr( 1 )
  val words = text.split( " " )
  words.map( word => ( word, title ) )
} )
// RDD[ ( String, String ) ]

// Now, if you want to print this...
yourRdd.foreach( { case ( word, title ) => println( s"{ $word, $title }" ) } )

// if you want to count ( this count is for non-unique words), 
val countRdd = yourRdd
  .groupBy( { case ( word, title ) => title } )  // group by title
  .map( { case ( title, iter ) => ( title, iter.size ) } ) // count for every title