Spark - How to handle error case in RDD.map() method correctly?

Question

I am trying to do some text processing using Spark RDD.

The format of the input file is:

2015-05-20T18:30 <some_url>/?<key1>=<value1>&<key2>=<value2>&...&<keyn>=<valuen>

I want to extract some fields from the text and convert them into CSV format like:

<value1>,<value5>,<valuek>,<valuen>

The following code is how I do this:

val lines = sc.textFile(s"s3n://${MY_BUCKET}/${MY_FOLDER}/test/*.gz")
val records = lines.map { line =>
    val mp = line.split("&")
                 .map(_.split("="))
                 .filter(_.length >= 2)
                 .map(t => (t(0), t(1))).toMap

    (mp.get("key1"), mp.get("key5"), mp.get("keyk"), mp.get("keyn"))
}

I would like to know that, if some line of the input text is of wrong format or invalid, then the map() function cannot return a valid value. This should very common in text processing, what is the best practice to deal with this problem?

Answer 1

in order to manage this errors you can use the scala's class Try within a flatMap operation, in code:

    val lines = sc.textFile(s"s3n://${MY_BUCKET}/${MY_FOLDER}/test/*.gz")
    val records = lines.flatMap (line =>
        Try{
          val mp = line.split("&")
              .map(_.split("="))
              .filter(_.length >= 2)
              .map(t => (t(0), t(1))).toMap

          (mp.get("key1"), mp.get("key5"), mp.get("keyk"), mp.get("keyn"))
      } match {
        case Success(map) => Seq(map)
        case _ => Seq()
    })

With this you have only the "good ones" but if you want both (the errors and the good ones) i would recommend to use a map function that returns a Scala Either and then use a Spark filter, in code:

    val lines = sc.textFile(s"s3n://${MY_BUCKET}/${MY_FOLDER}/test/*.gz")
    val goodBadRecords = lines.map (line =>
        Try{
          val mp = line.split("&")
              .map(_.split("="))
              .filter(_.length >= 2)
              .map(t => (t(0), t(1))).toMap

          (mp.get("key1"), mp.get("key5"), mp.get("keyk"), mp.get("keyn"))
      } match {
        case Success(map) => Right(map)
        case Failure(e) => Left(e)
    })
    val records = goodBadRecords.filter(_.isRight)
    val errors = goodBadRecords.filter(_.isLeft)

I hope this will be useful