How to setup csv component to map list of strings

Question

I have a csv file that holds country names and years they won on the eurovision:

country, year
Israel, 1998
Sweden, 2012
Sweden, 2015
United Kingdom, 1997

and my csv (using tototoshi):

object CountryEurovision {

  def countrEurovisionYearFile: File =  new File("conf/countryEurovision.csv")

  lazy val countrEurovisionYearMap: Map[String, String] = getConvertData

  private def getConvertData: Map[String, String] = {

    implicit object CodesFormat extends CSVFormat {
      val delimiter: Char = ','
      val quoteChar: Char = '"'
      val escapeChar: Char = '"'
      val lineTerminator: String = "\r\n"
      val quoting: Quoting = QUOTE_NONNUMERIC
      val treatEmptyLineAsNil: Boolean = false
    }

    val csvDataReader = CSVReader.open(countrEurovisionYearFile, "UTF-8")(CodesFormat)
    val linesIterator = csvDataReader.iteratorWithHeaders
    val convertedData = linesIterator.map { 
      row => row("Country") -> row("Year")
    }.toMap
    csvDataReader.close()
    convertedData
  }
}

now, since the country and year is not unique, cause a country can have several years when they won, so when I get Sweden:

CountryEurovision.countrEurovisionYearMap.get("Sweden")

I only get option res0: Option[String] = Some(2015) which I would expect to be the list of years per country... even if it's a country of just one year I will get a list, and in case of Sweden I will get list of 2012 and 2015...

How can I change my setup for that behavior?

Xavier Guihot · Accepted Answer · 2018-05-06 14:42:33Z

1

When you transform linesIterator.map { row => row("Country") -> row("Year") } into a Map with .toMap, for duplicated keys only the last one will be kept as it will override the previous one.

You can change this by having a unique element per key (country) by grouping values (dates) per key (before applying toMap) and modifying the value of your Map to be a List:

linesIterator
  .map { row => row("Country") -> row("Year") } // List(("Sweden", 1997), ("France", 2008), ("Sweden", 2017))
  .groupBy(_._1) // Map(France -> List((France,2008)), Sweden -> List((Sweden,1997), (Sweden,2017)))
  .mapValues(_.map(_._2)) // Map(France -> List(2008), Sweden -> List(1997, 2017))
  .toMap

which produces:

Map(France -> List(2008), Sweden -> List(1997, 2017))

This way, .get("Sweden") will return Some(List(1997, 2017)).

edited May 6, 2018 at 14:42

answered May 6, 2018 at 14:36

Xavier Guihot

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1 Comment

MNY Over a year ago

figured it out, i had to do .toList and then .groupBy

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