Scala function does not return a value

Question

I think I understand the rules of implicit returns but I can't figure out why splithead is not being set. This code is run via

val m = new TaxiModel(sc, file) 

and then I expect

m.splithead

to give me an array strings. Note head is an array of strings.

import org.apache.spark.SparkContext
import org.apache.spark.rdd.RDD

class TaxiModel(sc: SparkContext, dat: String) {
  val rawData = sc.textFile(dat)

  val head = rawData.take(10)
  val splithead = head.slice(1,11).foreach(splitData)

  def splitData(dat: String): Array[String] = {
    val splits = dat.split("\",\"")
    val split0 = splits(0).substring(1, splits(0).length)
    val split8 = splits(8).substring(0, splits(8).length - 1)
    Array(split0).union(splits.slice(1, 8)).union(Array(split8))
  }
}

Answer 1

foreach just evaluates expression, and do not collect any data while iterating. You probably need map or flatMap (see docs here )

head.slice(1,11).map(splitData) // gives you Array[Array[String]]

head.slice(1,11).flatMap(splitData) // gives you Array[String]

Answer 2

Consider also a for comprehension (which desugars in this case into flatMap ),

for (s <- head.slice(1,11)) yield splitData(s)

Note also that Scala strings are equipped with ordered collections methods, thus

splits(0).substring(1, splits(0).length)

proves equivalent to any of the following

splits(0).drop(1)
splits(0).tail