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im trying to convert a scala list of eithers, as such:
List(Left(3),Left(4),Left(1),Left(5))
Into a either of a list Either[List[Int],Int] like this?
Left(3,4,1,5)
Only using flatmap, map or fold?
ive been hammering at it for a while now and can simply not make it work
Assumed:
val a = List(Left(1), Left(2), Left(3)) // for example
Then following will return a Left[List[Int]]:
Left(a.map(_.value))
// Left(List(1, 2, 3))
Then you can extract the values out of the list, which I don't thin is generally a good idea.
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Consider the following list(1,1,2,2,3,4,4,5,5) I want to print only 3. Since it is the unique one. Can someone help me with the Scala code.
It's not a Spark question, but this function would do it for Scala
def uniqueElems[T](lst: Seq[T]) = {
lst.groupBy(identity).collect { case v if v._2.length == 1 => v._2.head }
}
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Given that match will never be None,
Which style is better or can I improve the first?
val tmp = (cols.find(_(0) == id).get)
SomeClass(tmp(0), tmp(1))
cols.find(_(0) == id) match {
case Some(value)=> SomeClass(value(0), value(1))
case None=> NotFound("Given id not found")
}
Since this a question about style, my answer is that neither of these is the best style. Instead, just keep the value in the Option
val opt: Option[SomeClass] = cols.find(_(0) == id).map(v => SomeClass(v(0), v(1)))
Keep processing/testing inside the Option using foreach/exists etc. until you really need the bare value. There is a very rich set of methods on Option that covers most of the things that are needed.
If the rest of the code is structured well, you will likely find that the value never needs to be extracted in a separate operation.
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I want instance's array just like as follow;
var ExampleObj = List(10)(new Obj)
Then I want to use this as;
var (hoge0, hoge1) = ExampleObj(2)(foo0, foo1, foo2)
The (new Obj) makes type mismatch.
[error] found : unittest.Obj
[error] required: Int
I do package unittest for Obj class.
What I make misunderstand ?
Could you please point out that point and how to solve it ?
If I understood your question correctly, you're trying to create a List with 10 instances of Obj class?
It can be done using fill method, like that:
List.fill(10)(new Obj)
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I have java code shown below, how to convert it to scala?
feature.getFeatures()
.stream()
.filter(a -> a.getFeatureName().equals(feature))
.findFirst()
.map(f -> f.Accounts().contains(accountId))
.orElse(true);
Whenever you see filter or find chained with map, think collect or collectFirst
So something like this should work:
feature.getFeatures()
.collectFirst {
case f if f.getFeatureName().equals(feature) =>
f.Accounts().contains(accountId)
}.getOrElse(true)
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I'm putting some test cases and having lots of parameters yet it is cumbersome and not so easy to understand putting them into a liner in scala. I rather specify in a visually acceptable manner but correctly parse them in scala...
I would use String Interpolation to define the arguments such as below
val kafkaServers = "server1:9092,server2:9092"
val pleasentArgs = s"""
--master='spark://someserver'
--metricWindowSize=50
--outputDirectory='/tmp/someGoodDirectory'
--zkQuorum=$zkQuorum
--saveToHDF=false
--userName='jack#somewhereElse.com'
--kafkaServers=$kafkaServers
"""
And have a method to clean up all the newline, tab etc characters and then generate the args as shown below:
def cleanUp(str:String) = str.split('\n').map(_.trim.filter(_ >= ' ')).mkString(" ")
def genArgs(args:String): Array[String] =cleanUp(args).split(" ").filter(!_.trim.isEmpty)
So eventually we can just call genArgs method
val args = genArgs(pleasentArgs)