scala-collections

I would like to derive a version of a Scala built-in collection that expands on the functionality for a particular generic type e.g., import scala.collection.immutable._ class Tuple2Set[T1,T2] extends HashSet[Tuple2[T1,T2]] { def left = map ( _._1 ) def right = map ( _._2 ) } However when I try to use it with the following test new Tuple2Set[String,String]() + (("x","y")) left I get the following compile error error: value left is not a member of scala.collection.immutable.HashSet[(String, String)] How can I change the class so that this works? As Kevin Wright said, + operation will return

This question already has an answer here: Scala foreach strange behaviour 5 answers Scala lets you use an underscore to do a simple map. So for example instead of writing: def roleCall(people: String*){ people.toList.map(x => println(x)) } ...I can instead write: def roleCall(people: String*){ people.toList.map(println(_)) } However for some reason I can't write: def greet(people: String*){ // This won't compile! people.toList.map(println("Hello " + _)) } instead I have to write: def greet(people: String*){ people.toList.map(x => println("Hello " + x)) } Can anyone explain why? Basically, the

I have two files. One is scala and other is java. Scala file has a function which returns scala immutable map. Java file wants to use that map as dictionary. I am a newbie to scala and java. How can I convert that scala map to java dicionary? Use the static forwarders from Java. In Scala 2.13 the API is simplified, with overloaded asJava for conversion to Java: $ javap -cp ~/scala-2.13.0/lib/scala-library.jar scala.jdk.javaapi.CollectionConverters Compiled from "CollectionConverters.scala" public final class scala.jdk.javaapi.CollectionConverters { public static scala.collection.mutable.Map

I have a following method: def firstAndLast[CC, A, That](seq: CC)(implicit asSeq: CC => Seq[A], cbf: CanBuildFrom[CC, A, That]): That = { val b = cbf(seq) b += seq.head b += seq.last b.result } See: Method taking Seq[T] to return String rather than Seq[Char] for rationale. It works like a charm in the first case but fails to compile in the second: List("abc", "def") map {firstAndLast(_)} List("abc", "def") map firstAndLast Giving: error: No implicit view available from CC => Seq[A]. List("abc", "def") map firstAndLast Any idea how to improve this declaration to avoid extra wrapping? Seems like

In the Scala Collections framework, I think there are some behaviors that are counterintuitive when using map() . We can distinguish two kinds of transformations on (immutable) collections. Those whose implementation calls newBuilder to recreate the resulting collection, and those who go though an implicit CanBuildFrom to obtain the builder. The first category contains all transformations where the type of the contained elements does not change. They are, for example, filter , partition , drop , take , span , etc. These transformations are free to call newBuilder and to recreate the same

For a given Array[Double] , for instance val a = Array.tabulate(100){ _ => Random.nextDouble * 10 } what is a simple approach to calculate a histogram with n bins ? A very similar preparation of values as in @om-nom-nom 's answer, yet the histogram method quite small by using partition , case class Distribution(nBins: Int, data: List[Double]) { require(data.length > nBins) val Epsilon = 0.000001 val (max,min) = (data.max,data.min) val binWidth = (max - min) / nBins + Epsilon val bounds = (1 to nBins).map { x => min + binWidth * x }.toList def histo(bounds: List[Double], data: List[Double]):