Collection library for Scala Programming Language
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Questions tagged [scala-collections]
1639 questions
18
votes
1 answer
Why does Option not extend the Iterable trait directly?
Option is implicitly convertible to an Iterable - but why does it not just just implement Iterable directly:
def iterator = new Iterator[A] {
var end = !isDefined
def next() = {
val n = if (end) throw new NoSuchElementException() else get
…
oxbow_lakes
- 133,303
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18
votes
3 answers
Scala: "map" vs "foreach" - is there any reason to use "foreach" in practice?
In Scala collections, if one wants to iterate over a collection (without returning results, i.e. doing a side effect on every element of collection), it can be done either with
final def foreach(f: (A) ⇒ Unit): Unit
or
final def map[B](f: (A) ⇒ B):…
GreyCat
- 16,622
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- 112
18
votes
2 answers
Scala create List[Int]
How can I quickly create a List[Int] that has 1 to 100 in it?
I tried List(0 to 100), but it returns List[Range.Inclusive]
Thanks
Lydon Ch
- 8,637
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18
votes
1 answer
Scala: Parallel collection in object initializer causes a program to hang
I've just noticed a disturbing behavior.
Let's say I have a standalone program consisting of a sole object:
object ParCollectionInInitializerTest {
def doSomething { println("Doing something") }
for (i <- (1 to 2).par) {
println("Inside…
Lukasz Gieron
- 276
- 2
- 12
17
votes
4 answers
Maximum Length for scala queue
I'm curious if Scala has some gem hidden in its collection classes that I can use. Basically I'm looking for something like a FIFO queue, but that has an upper-limit on its size such that when the limit is hit, the oldest (first) element is removed…
John S
- 1,695
- 2
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17
votes
1 answer
Parallelize Scala's Iterator
Please note: This is not a duplicate question, since this question specifies on all methods Iterator has, not just map and flatMap. Therefore Future.traverse are not a good answer.
Let's say I have this simple statement:
(1 to…
Rok Kralj
- 46,826
- 10
- 71
- 80
17
votes
2 answers
How to use priority queues in Scala?
I am trying to implement A* search in Scala (version 2.10), but I've ran into a brick wall - I can't figure out how to use Scala's Priority Queue.
I have a set of squares, represented by (Int, Int)s, and I need to insert them with priorities…
Antimony
- 37,781
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17
votes
5 answers
How to convert a nested scala collection to a nested Java collection
I'm having compilation issues between Scala and Java.
My Java code needs a
java.util.Map>
My scala code has a
Map[Double, Vector[Foo]]
I get the compilation error:
error: type mismatch;
found :…
Adam K
- 233
- 2
- 7
16
votes
2 answers
Why does Iterator have a contains method but Iterable does not, in Scala 2.8?
I would like to call 'contains' on my Iterables :-)
adam77
- 2,797
- 3
- 21
- 29
16
votes
4 answers
Parallel iterator in Scala
Is it somehow possible, using Scala's parallel collections to parallelize an Iterator without evaluating it completely beforehand?
Here I am talking about parallelizing the functional transformations on an Iterator, namely map and flatMap.
I think…
ziggystar
- 28,410
- 9
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15
votes
3 answers
Inconsistent behaviour for xs.sliding(n) if n is less than size?
According to scaladoc, sliding() returns...
"An iterator producing iterable collections of size size, except the last and the only element will be truncated if there are fewer elements than size."
For me, intuitivelly, sliding(n) would return a…
Adrian
- 3,762
- 2
- 31
- 40
15
votes
3 answers
How to make method return the same generic as the input?
I want to split a string delimited by commas and use the result as either a Seq or a Set:
def splitByComma(commaDelimited: String): Array[String]
= commaDelimited.trim.split(',')
def splitByCommaAsSet(commaDelimited: String): Set[String]
=…
yhylord
- 430
- 4
- 13
15
votes
7 answers
Scala: How to create a Map[K,V] from a Set[K] and a function from K to V?
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:…
aioobe
- 413,195
- 112
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- 826
15
votes
4 answers
What is the proper way to remove elements from a scala mutable map using a predicate
How to do that without creating any new collections? Is there something better than this?
val m = scala.collection.mutable.Map[String, Long]("1" -> 1, "2" -> 2, "3" -> 3, "4" -> 4)
m.foreach(t => if (t._2 % 2 == 0) m.remove(t._1))
println(m)
P.S.…
Oleg Galako
- 1,036
- 1
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- 16
15
votes
3 answers
Check if a key exists in play.api.libs.json.Json
contains like functionality for play.api.libs.json.Json
val data=Map("id" -> "240190", "password" -> "password","email" -> "email@domain.com")
data.contains("email")//true
val info=Json.obj("id" -> "240190", "password" -> "password","email" ->…
Govind Singh
- 15,282
- 14
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