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scalaseqeither

Project a sequence of 'Left's from a sequence of Eithers?

(Caveat - I'm a scala noob) Given a sequence of Eithers, viz 

theResults : Seq[Either[Error, String]]

I am trying to extract all the Errors by using a map on the left(s)

theResults match {
  case r if r.exists(_.isLeft)  => {
    val errors = theResults.map(r => r.left)
    ...
  }

However, this returns 

Seq[Either.LeftProjection[ErrorResponse, String]]

Instead of the Seq[ErrorResponse] as I was hoping for.

Please put me out of my misery?

Solution

  • The easiest option would probably be:

    val lefts = theResults.map(_.left.toOption).flatten

    which will return a sequence of Error (or whatever the left type is).

    Personally, I think that scalaz Either is nicer to work with, as it's right-biased...