scala-collections

问题 I have a folder structure like below: - main -- java -- resources -- scalaresources --- commandFiles and in that folders I have my files that I have to read. Here is the code: def readData(runtype: String, snmphost: String, comstring: String, specificType: String): Unit = { val realOrInvFile = "/commandFiles/snmpcmds." +runtype.trim // these files are under commandFiles folder, which I have to read. try { if (specificType.equalsIgnoreCase("Cisco")) { val specificDeviceFile: String = "

问题 There is some data that I have pulled from a remote API, for which I use a Future-style interface. The data is structured as a linked-list. A relevant example data container is shown below. case class Data(information: Int) { def hasNext: Boolean = ??? // Implemented def next: Future[Data] = ??? // Implemented } Now I'm interested in adding some functionality to the data class, such as map , foreach , reduce , etc. To do so I want to implement some form of IterableLike such that it inherets

问题 In immutable collection of SCALA a new object is created when length of collection changes Let us suppose I create a immutable Map and then perform concatenation. CODE=> object Dcoder extends App { var map=Map("abc"-> 1,"xyz"->2) var change =map++Map("change of object"+>3) } Now my Question is a) Does the new object gets created because of ++ ?? b) Since I'm using a IMMUTABLE COLLECTION and length of Immutable collection has changed so new object is created ?? 回答1: From the documentation of +

问题 Not very familiar with Scala's type system, but here's what I'm trying to do. I have a function that tries to filter people by first and last name, and if that fails filters by first name only. case class Person(id: Int, first: String, last:String) def(people: Set[Person], firstName: String, lastName: String): (MatchResult, Set[Person]) = val (both, firstOnly) = people.filter(_.first == firstName).partition(_.last == lastName) (both.nonEmpty, firstOnly.nonEmpty) match { case (true, _) =>

问题 User Régis Jean-Gilles gracefully answered my previous question where I was struggling with CanBuildFrom and enrichment functions (aka "pimp my library" or "enrich my library"): Creating an implicit function that wraps map() in Scala with the right type: Not for the faint at heart But this time I've got an even more complicated issue. I have a function to implement variations on intersectWith , for intersecting collections by their keys. I've managed to make them work like proper collection

问题 I started to receive this kind of error in my code: Message: java.lang.NoSuchMethodError:scala.collection.JavaConversions $.asScalaSet(Ljava/util/Set;)Lscala/collection/mutable/Set and then I see a long screen of stacktrace of uninteresting nature, which is triggered on this piece of code: edited.authors.toSeq where authors is a java.lang.Set . Does anybody know why is this happening? It's a runtime failure and not a compile one. 回答1: You are using a library which has been compiled with 2.8.1

问题 The signature of reduceLeft on some Seq[A] is def reduceLeft [B >: A] (f: (B, A) => B): B The type of A is known, but the lower bound >: tells us that B can be any supertype of A . Why is it like this? Why not def reduceLeft (f: (A, A) => A): A We already know that the head of the sequence is type A and so I can't think of how B could be anything other than equal to A . Can you provide an example where B is some super-type? 回答1: Let's say your class B has a method combine(other:B): B . Now

问题 In Scala, test("Appending a tuple to a Buffer"){ val buffer = ArrayBuffer[Int]() val aTuple = (2, 3) println(buffer += (2, 3)) // Result : ArrayBuffer(2, 3) println(buffer += aTuple ) // doesn't compile } Why does line println(buffer += (2, 3)) work, but line println(buffer += aTuple ) not compile ? 回答1: Because you are not adding a Tuple , you are calling the += method with two parameters: buffer += (3, 4) // is equivalent here to buffer.+=(3, 4) And that method is defined both with varargs

问题 I am trying to sort a collection of linked-list nodes. The collection contains nodes from more than one linked list; ordering must be maintained within each list, but ordering across lists does not matter. PartialOrdering[T] seems like the natural choice, but I cannot find any standard functions within Scala that support it (e.g. .sort only takes Ordering[T] ). I've considered wrapping the former type into the latter, but realise this will actually produce erroneous results. Partial ordering

问题 I have a simple task here: break a Set of n elements into m Sets based on a batch size - typically I'll want to limit my sub-Sets to 1,000 elements. I wrote something like this, where input is the master, large collection: var strings = Set[String]() ++ input var sets = List[Set[String]]() while (!strings.isEmpty) { val (head, rest) = strings.splitAt(100) sets = sets :+ head securities = rest } which works fine, but I am thinking there HAS to be a more elegant/functional solution to such a