Tuesday, June 12, 2012

Parsing CSVs in Scala

I did a quick google on parsing CSVs in Scala, and one of the top hits was a stack overflow question where the answer was wrong.  Very wrong.  So, I threw together a quick parser in Scala to get the job done.  I'm not saying it's good, but it passes the spec tests I have included quotes and quoted commas both with single and double quotes.  I hope this is useful, and perhaps somebody can improve upon it.

object CSVParser extends RegexParsers {
  def apply(f: java.io.File): Iterator[List[String]] = io.Source.fromFile(f).getLines().map(apply(_))
  def apply(s: String): List[String] = parseAll(fromCsv, s) match {
    case Success(result, _) => result
    case failure: NoSuccess => {throw new Exception("Parse Failed")}

  def fromCsv:Parser[List[String]] = rep1(mainToken) ^^ {case x => x}
  def mainToken = (doubleQuotedTerm | singleQuotedTerm | unquotedTerm) <~ ",?".r ^^ {case a => a}
  def doubleQuotedTerm: Parser[String] = "\"" ~> "[^\"]+".r <~ "\"" ^^ {case a => (""/:a)(_+_)}
  def singleQuotedTerm = "'" ~> "[^']+".r <~ "'" ^^ {case a => (""/:a)(_+_)}
  def unquotedTerm = "[^,]+".r ^^ {case a => (""/:a)(_+_)}

  override def skipWhitespace = false

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