scala-collections

问题 I have a java map: java.util.Map<SomeObject, java.util.Collection<OtherObject>> and I would like to convert it to the scala map: Map[SomeObject, Set[OtherObject]] I have used mapAsScalaMap but the result is not quite what I want, the result is: Map[SomeObject, java.util.Collection[OtherObject]] . How can I fix it to also convert the collection to a set? NOTE: actually my original problem was to convert google's ArrayListMultimap<SomeObject, OtherObject> to a MultiMap[SomeObject, OtherObject]

问题 I have a java map: java.util.Map<SomeObject, java.util.Collection<OtherObject>> and I would like to convert it to the scala map: Map[SomeObject, Set[OtherObject]] I have used mapAsScalaMap but the result is not quite what I want, the result is: Map[SomeObject, java.util.Collection[OtherObject]] . How can I fix it to also convert the collection to a set? NOTE: actually my original problem was to convert google's ArrayListMultimap<SomeObject, OtherObject> to a MultiMap[SomeObject, OtherObject]

问题 When I am trying parse the json object I am getting the below error. import net.liftweb.json._ object SarahEmailPluginConfigTest { implicit val formats = DefaultFormats case class Mailserver(url: String, username: String, password: String) val json = parse("""{"url": "imap.yahoo.com", "username": "myusername", "password": "mypassword" }""") def main(args: Array[String]) { val m = json.extract[Mailserver] println(m.url) println(m.username) println(m.password) } } I have added "lift-json_2.9.0

问题 This question already has answers here : Finding type parameters via reflection in Scala 2.10? (2 answers) Closed 5 years ago . Suppose I get a Type representing List[Int]: > import scala.reflect.runtime.universe > val mirror = universe.runtimeMirror(this.getClass.getClassLoader) mirror: reflect.runtime.universe.Mirror = JavaMirror with ... > class X{ def getList():List[Int] = null } defined class X > val method = mirror. classSymbol(classOf[X]). toType. declarations. filter{_.isMethod}. map{

问题 I can do this quite easily, and cleanly, using a for loop. For instance, if I wanted to traverse a Seq from every element back to itself I would do the following: val seq = Seq(1,2,3,4,5) for (i <- seq.indices) { for (j <- seq.indices) { print(seq(i + j % seq.length)) } } But as I'm looking to fold over the collection, I'm wondering if there is a more idiomatic approach. A recursive approach would allow me to avoid any var s. But basically, I'm wondering if something like the following is

问题 I wonder why List(3,2,1).toIndexedSeq.sortBy(x=>x) doesn't work: scala> List(3,2,1).toIndexedSeq.sortBy(x=>x) // Wrong <console>:8: error: missing parameter type List(3,2,1).toIndexedSeq.sortBy(x=>x) ^ <console>:8: error: diverging implicit expansion for type scala.math.Ordering[B] starting with method Tuple9 in object Ordering List(3,2,1).toIndexedSeq.sortBy(x=>x) ^ scala> Vector(3,2,1).sortBy(x=>x) // OK res: scala.collection.immutable.Vector[Int] = Vector(1, 2, 3) scala> Vector(3,2,1)

问题 For any given list or array, for instance val list = (1 to 3).toList val array = (1 to 3).toArray and a given function that maps from and onto the collection type, for instance def f(v: Int): Int = v + 10 how to apply f to the ith element of list or array so that list.myApply(f, ith = 2) res: List(1,12,3) and also array.myApply(f, ith = 2) res: Array(1,12,3) 回答1: tl;dr import scala.collection.SeqLike import scala.collection.generic.CanBuildFrom implicit class Seq_[A, Repr, S : ({type L[X] = X

问题 I am looking for an approach to join multiple Lists in the following manner: ListA a b c ListB 1 2 3 4 ListC + # * § % .. .. .. Resulting List: a 1 + b 2 # c 3 * 4 § % In Words: The elements in sequential order, starting at first list combined into the resulting list. An arbitrary amount of input lists could be there varying in length. I used multiple approaches with variants of zip, sliding iterators but none worked and especially took care of varying list lengths. There has to be an elegant

问题 Let's say I have two optional Ints (both can be Some or None): val one : Option[Int] = Some(1) val two : Option[Int] = Some(2) My question is the following: Are there any intelligent way to sum them op using Scalas brilliant collection-methods? I realize that I could merge them into a collection, flatten it and use reduceLeftOption like so: (one :: two :: Nil).flatten.reduceLeftOption(_ + _) // Some(3) But, the solution above means creating a new collection, and living in a rich and developed

问题 What is the best way to create a Map[K,V] from a Set[K] and function from K to V ? For example, suppose I have scala> val s = Set(2, 3, 5) s: scala.collection.immutable.Set[Int] = Set(2, 3, 5) and scala> def func(i: Int) = "" + i + i func: (i: Int)java.lang.String What is the easiest way of creating a Map[Int, String](2 -> "22", 3 -> "33", 5 -> "55") 回答1: You can use foldLeft : val func2 = (r: Map[Int,String], i: Int) => r + (i -> func(i)) s.foldLeft(Map.empty[Int,String])(func2) This will