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Questions tagged [scala-collections]

Collection library for Scala Programming Language

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1639 questions
47
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4 answers

how to remove key value from map in scala

Map(data -> "sumi", rel -> 2, privacy -> 0, status -> 1,name->"govind singh") how to remove data from this map , if privacy is 0. Map(rel -> 2, privacy -> 0, status -> 1,name->"govind singh")
Govind Singh
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mutable vs. immutable in Scala collections

I am fairly new to Scala and am trying to understand the collections hierarchy. I see that there is a distinction between 'mutable' and 'immutable' collections, but I don't understand what this actually means at the implementation level and how…
astay13
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Scala convert Iterable or collection.Seq to collection.immutable.Seq

It appears the toSeq method in Scala collections returns a scala.collection.Seq, I could also return a Traversable or Iterable but need to convert this to a scala.collection.immutable.Seq. Is there an easy way to do this? Thanks Richard
Richard Todd
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remove first and last Element from scala.collection.immutable.Iterable[String]

I am trying to convert my way of getting values from Form, but stuck some where val os= for { m <- request.body.asFormUrlEncoded v <- m._2 } yield v os is scala.collection.immutable.Iterable[String] and when i print it in console os map…
Govind Singh
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How to define an Ordering in Scala?

Having val hm: HashMap[org.joda.time.DateTime, MyType] I am trying to get the first and the last DateTime of the set by means of hm.keys.min and hm.keys.max respectively but the compiler says No implicit Ordering defined for org.joda.time.DateTime.…
Ivan
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Why is zipped faster than zip in Scala?

I have written some Scala code to perform an element-wise operation on a collection. Here I defined two methods that perform the same task. One method uses zip and the other uses zipped. def ES (arr :Array[Double], arr1 :Array[Double])…
Asif
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Scala foldLeft on Maps

How do you use Map.foldLeft? According to the docs it looks like foldLeft [B] (z: B)(op: (B, (A, B)) ⇒ B) : B But I'm having difficulty: Map("first"->1,"second"->2).foldLeft(0)((a,(k,v)) => a+v ) error: not a legal formal parameter The error…
Pengin
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2 answers

scala parallel collections degree of parallelism

Is there any equivalent in scala parallel collections to LINQ's withDegreeOfParallelism which sets the number of threads which will run a query? I want to run an operation in parallel which needs to have a set number of threads running.
Steve Severance
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7 answers

How to find duplicates in a list?

I have a list of unsorted integers and I want to find those elements which have duplicates. val dup = List(1,1,1,2,3,4,5,5,6,100,101,101,102) I can find the distinct elements of the set with dup.distinct, so I wrote my answer as follows. val dup =…
Phil
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Scala for loop over two lists simultaneously

I have a List[Message] and a List[Author] which have the same number of items, and should be ordered so that at each index, the Message is from the Author. I also have class that we'll call here SmartMessage, with a constructor taking 2 arguments: a…
Blackbird
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39
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Scala: how to merge a collection of Maps

I have a List of Map[String, Double], and I'd like to merge their contents into a single Map[String, Double]. How should I do this in an idiomatic way? I imagine that I should be able to do this with a fold. Something like: val newMap =…
Jeff
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Difference between mapValues and transform in Map

In Scala Map (see API) what is the difference in semantics and performance between mapValues and transform ? For any given map, for instance val m = Map( "a" -> 2, "b" -> 3 ) both m.mapValues(_ * 5) m.transform( (k,v) => v * 5 ) deliver the same…
elm
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Difference between MutableList and ListBuffer

What is the difference between Scala's MutableList and ListBuffer classes in scala.collection.mutable? When would you use one vs the other? My use case is having a linear sequence where I can efficiently remove the first element, prepend, and…
Mike
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Semantics of Scala Traversable, Iterable, Sequence, Stream and View?

There are other questions such as Scala: What is the difference between Traversable and Iterable traits in Scala collections? and How would I get the sum of squares of two Lists in Scala? that answers the question partially. I felt a question that…
smartnut007
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how to sort a scala.collection.Map[java.lang.String, Int] by its values?

How would you sort a scala.collection.Map[java.lang.String, Int] by its values (so on the Int)? What is a short and elegant way to do that?
Jan Willem Tulp
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