Convert List[Either[A, B]] to Either[List[A], List[B]]

Question

How to convert List[Either[String, Int]] to Either[List[String], List[Int]] using a method similar to cats sequence? For example, xs.sequenc

Answer 1

Try

xs.traverse(_.toValidated.bimap(List(_), identity)).toEither

// List(Left("error1"), Left("error2")) => Left(List("error1", "error2"))
// List(Right(10), Right(20))           => Right(List(10, 20))
// List(Right(10), Left("error2"))      => Left(List("error2"))