Option in the Scala language is a container for zero or one element of a given type.
Option in scala is a container for zero or one element of a given type.
Questions tagged [scala-option]
232 questions
127
votes
4 answers
How to filter None's out of List[Option]?
If I have a List[Option[A]] in Scala, what is the idiomatic way to filter out the None values?
One way is to use the following:
val someList: List[Option[String]] = List(Some("Hello"), None, Some("Goodbye"))
someList.filter(_ != None)
Is there a…
Ralph
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119
votes
4 answers
Wrapping null-returning method in Java with Option in Scala?
Suppose I have a method session.get(str: String): String but you don't know whether it will return you a string or a null, because it comes from Java.
Is there an easier way to treat this in Scala instead of session.get("foo") == null ? Maybe some…
José Leal
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85
votes
5 answers
Composing Option with List in for-comprehension gives type mismatch depending on order
Why does this construction cause a Type Mismatch error in Scala?
for (first <- Some(1); second <- List(1,2,3)) yield (first,second)
:6: error: type mismatch;
found : List[(Int, Int)]
required: Option[?]
for (first <- Some(1);…
Felipe Kamakura
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77
votes
2 answers
How to transform Scala collection of Option[X] to collection of X
I'm starting to explore Scala, and one of the things I'm intrigued by is the Option type and the promise of being able to eliminate null related errors.
However I haven't been able to work out how to transform a list (or other collection) of, say,…
npad
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75
votes
4 answers
Is there a scala identity function?
If I have something like a List[Option[A]] and I want to convert this into a List[A], the standard way is to use flatMap:
scala> val l = List(Some("Hello"), None, Some("World"))
l: List[Option[java.lang.String]] = List(Some(Hello), None,…
oxbow_lakes
- 133,303
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74
votes
1 answer
How to get an Option from index in Collection in Scala?
Is there a way, only using the Scala collection API, to get an Option in a List when trying to get an element by its index?
I'm looking for the equivalent of this function, does it exist?
def optionalValue[T](l: List[T], index: Int) = {
if (l.size…
Loic
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48
votes
6 answers
Why is foreach better than get for Scala Options?
Why using foreach, map, flatMap etc. are considered better than using get for Scala Options? If I useisEmpty I can call get safely.
Michael
- 10,185
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46
votes
4 answers
Scala: convert string to Int or None
I am trying to get a number out of an xml field
...
12
...
via
Some((recipe \ "Main" \ "Quantity").text.toInt)
Sometimes there may not be a value in the xml, though. The text will be "" and this throws an…
doub1ejack
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43
votes
6 answers
Why Some(null) isn't considered None?
I am curious:
scala> Some(null) == None
res10: Boolean = false
Why isn't Some(null) transformed to None?
Geo
- 93,257
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41
votes
6 answers
Un-optioning an optioned Option
Say I have a val s: Option[Option[String]]. It can thus have the following values:
Some(Some("foo"))
Some(None)
None
I want to reduce it so that the first becomes Some("foo") while the two others become None. Obviously there are many ways to…
Knut Arne Vedaa
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40
votes
2 answers
How to flatten list of options using higher order functions?
Using Scala 2.7.7:
If I have a list of Options, I can flatten them using a for-comprehension:
val listOfOptions = List(None, Some("hi"), None)
listOfOptions: List[Option[java.lang.String]] = List(None, Some(hi), None)
scala> for (opt <-…
Synesso
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38
votes
6 answers
Could/should an implicit conversion from T to Option[T] be added/created in Scala?
Is this an opportunity to make things a bit more efficient (for the prorammer): I find it gets a bit tiresome having to wrap things in Some, e.g. Some(5). What about something like this:
implicit def T2OptionT( x : T) : Option[T] = if ( x == null )…
waterlooalex
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35
votes
4 answers
Why doesn't Option have a fold method?
I wonder why scala.Option doesn't have a method fold like this defined:
fold(ifSome: A => B , ifNone: => B)
equivalent to
map(ifSome).getOrElse(ifNone)
Is there no better than using map + getOrElse?
soc
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34
votes
9 answers
Check if a string is blank or doesn't exist in Scala
I have an Option[String].
I want to check if there is a string exists and if it's exists its not blank.
def isBlank( input : Option[String]) : Boolean =
{
input.isEmpty ||
input.filter(_.trim.length > 0).isEmpty
}
Is there is a…
Soumya Simanta
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33
votes
3 answers
Convert Option to Either in Scala
Suppose I need to convert Option[Int] to Either[String, Int] in Scala. I'd like to do it like this:
def foo(ox: Option[Int]): Either[String, Int] =
ox.fold(Left("No number")) {x => Right(x)}
Unfortunately the code above doesn't compile and I need…
Michael
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