I have a list of Person and want to retrieve a person by its id
val person = personL.find(_.id.equals(tempId))
After that, I want to get as a tuple the first and last element of a list which is an attribute of Person.
val marks: Option[(Option[String], Option[String])] = person.map { p =>
val marks = p.school.marks
(marks.headOption.map(_.midtermMark), marks.lastOption.map(_.finalMark))
}
This work's fine but now I want to transform the Option[(Option[String], Option[String])] to a simple (Option[String], Option[String]). Is it somehow possible to do this on-the-fly by using the previous map?
I suppose:
person.map{...}.getOrElse((None, None))
(None, None) is a default value here in case if your option of tuple is empty
You are, probably, looking for fold:
personL
.collectFirst {
case Person(`tempId`, _, .., school) => school.marks
}.fold[Option[String], Option[String]](None -> None) { marks =>
marks.headOption.map(_.midtermMark) -> marks.lastOption.map(_.finalMark)
}
Related
A Scala map contains a key X.
The value can be either an array of Strings Array("Y")
or a simple String object, "Y".
I need to retrieve the value from the map and test
if the value is a string,
mayMap("X")=="Y"
or, if the value is an array.
myMap("X").contains("Y")
I don't want to use an if statement statement to check the type first of the value first of all. One option would be to write a function which checks the value, if it is an array then return the array, otherwise create an array with the single string element contained in the map. Then the call would be:
myToArrayFunction(myMap("X")).contains("Y")
That's what I actually do in Java.
But this is Scala. Is there a better idiom to do this in one line using pre-existing functions?
This should work:
myMap.get("X") match {
case None => println("oh snap!")
case Some(x) => x match {
case i: String => println(s"hooray for my String $i") // do something with your String here
case a: Array[String] => println(s"It's an Array $a") // do something with your Array here
}
}
case class Y(name: String)
//val a = Map[String, Any]("X" -> "Y")
val a = Map[String, Any]("X" -> Y("Peter"))
a.getOrElse("X", "Default") match {
case s: String => println(s)
case Y(name) => println(name)
}
you can also use something like this:
//val a = Map[String, Any]("X" -> "Y")
val a = Map[String, Any]("X" -> Y("Peter"))
a.map(v => println(v._2))
I have Some() type Map[String, String], such as
Array[Option[Any]] = Array(Some(Map(String, String)
I want to return it as
Array(Map(String, String))
I've tried few different ways of extracting it-
Let's say if
val x = Array(Some(Map(String, String)
val x1 = for (i <- 0 until x.length) yield { x.apply(i) }
but this returns IndexedSeq(Some(Map)), which is not what I want.
I tried pattern matching,
x.foreach { i =>
i match {
case Some(value) => value
case _ => println("nothing") }}
another thing I tried that was somewhat successful was that
x.apply(0).get.asInstanceOf[Map[String, String]]
will do something what I want, but it only gets 0th index of the entire array and I'd want all the maps in the array.
How can I extract Map type out of Some?
If you want an Array[Any] from your Array[Option[Any]], you can use this for expression:
for {
opt <- x
value <- opt
} yield value
This will put the values of all the non-empty Options inside a new array.
It is equivalent to this:
x.flatMap(_.toArray[Any])
Here, all options will be converted to an array of either 0 or 1 element. All these arrays will then be flattened back to one single array containing all the values.
Generally, the pattern is either to use transformations on the Option[T], like map, flatMap, filter, etc.
The problem is, we'll need to add a type cast to retrieve the underlying Map[String, String] from Any. So we'll use flatten to remove any potentially None types and unwrap the Option, and asInstanceOf to retreive the type:
scala> val y = Array(Some(Map("1" -> "1")), Some(Map("2" -> "2")), None)
y: Array[Option[scala.collection.immutable.Map[String,String]]] = Array(Some(Map(1 -> 1)), Some(Map(2 -> 2)), None)
scala> y.flatten.map(_.asInstanceOf[Map[String, String]])
res7: Array[Map[String,String]] = Array(Map(1 -> 1), Map(2 -> 2))
Also when you talk just about single value you can try Some("test").head and for null simply Some(null).flatten
I have the following input string:
"0.3215,Some(0.5123)"
I would like to retrieve the tuple (0.3215,Some(0.5123)) with: (BigDecimal,Option[BigDecimal]).
Here is one of the thing I tried so far:
"\\d+\\.\\d+,Some\\(\\d+\\.\\d+".r findFirstIn iData match {
case None => Map[BigDecimal, Option[BigDecimal]]()
case Some(s) => {
val oO = s.split(",Some\\(")
BigDecimal.valueOf(oO(0).toDouble) -> Option[BigDecimal](BigDecimal.valueOf(lSTmp2(1).toDouble))
}
}
Using a Map and transforming it into a tuple.
When I try directly the tuple I get an Equals or an Object.
Must miss something here...
Your code has several issues, but the big one seems to be that the case None side of the match returns a Map but the Some(s) side returns a Tuple2. Map and Tuple2 unify to their lowest-common-supertype, Equals, which is what you're seeing.
I think this is what you're trying to achieve?
val Pattern = "(\\d+\\.\\d+),Some\\((\\d+\\.\\d+)\\)".r
val s = "0.3215,Some(0.5123)"
s match {
case Pattern(a,b) => Map(BigDecimal(a) -> Some(BigDecimal(b)))
case _ => Map[BigDecimal, Option[BigDecimal]]()
}
// Map[BigDecimal,Option[BigDecimal]] = Map(0.3215 -> Some(0.5123))
I have a list of strings as shown below, which lists fruits and the cost associated with each. In case of no value, it is assumed to be 5:
val stringList: List[String] = List("apples 20", "oranges", "pears 10")
Now I want to split the string to get tuples of the fruit and the cost. What is the scala way of doing this?
stringList.map(query => query.split(" "))
is not what I want.
I found this which is similar. What is the correct Scala way of doing this?
You could use a regular expression and pattern matching:
val Pat = """(.+)\s(\d+)""".r // word followed by whitespace followed by number
def extract(in: String): (String, Int) = in match {
case Pat(name, price) => (name, price.toInt)
case _ => (in, 5)
}
val stringList: List[String] = List("apples 20", "oranges", "pears 10")
stringList.map(extract) // List((apples,20), (oranges,5), (pears,10))
You have two capturing groups in the pattern. These will be extracted as strings, so you have to convert explicitly using .toInt.
You almost have it:
stringList.map(query => query.split(" "))
is what you want, just add another map to it to change lists to tuples:
.map { list => list.head -> list.lift(1).getOrElse("5").toInt }
or this instead, if you prefer:
.collect {
case Seq(a, b) => a -> b.toInt
case Seq(a) => a -> 5
}
(.collect will silently ignore the occurrences, where there are less than one or more than two elements in the list. You can replace it with .map if you would prefer it to through an error in such cases).
I have following list:
val list = List(("name1",20),("name2",20),("name1",30),("name2",30),
("name3",40),("name3",30),("name3",20))
I want following output:
List(("name3",40))
I tried following:
val distElements = list.map(_._2).distinct
list.groupBy(_._1).map{ case(k,v) =>
val h = v.map(_._2)
if(distElements.equals(h)) List.empty else distElements.diff(h)
}.flatten
But this is not I am looking for.
Can anybody give answer/hint me to get expected output.
I understand the question as looking for the element of the list whose _2 (number) occurs only once.
val list = List(("name1",20),("name2",20),("name1",30),("name2",30),
("name3",40),("name3",30),("name3",20))
First you group by the _2 element, which gives you a map whose keys are lists of all elements with the same _2:
val g = list.groupBy(_._2) // Map[Int, List[(String, Int)]]
Now you can filter those entries that consists only of one element:
val opt = g.collectFirst { // Option[(String, Int)]
case (_, single :: Nil) => single
}
Or (if you are expecting possibly more than one distinct value)
val col = g.collect { // Map[String, Int]
case (_, single :: Nil) => single
}
Seems to me that you're looking to match against both the value of the left hand and the right hand at the same time while also preserving the type of collection you're looking at, a List. I would use collect:
val out = myList.collect{
case item # ("name3", 40) => item
}
which combines a PartialFunction with filter and map like qualities. In this case, it filters out any value for which the PartialFunction is not defined while mapping the values which match. Here, I've only allowed for a singular match.