could you help me concerning a basic question?
I have a list of "Rdv" (meetings) where Rdv is a case class having 3 fields storing phone numbers as Strings: telBureau, telPortable & TelPrivé.
I get this list from slick, via a native SQL query; this query fills the 3 phone number fields with either a String or "null"(a null object, not the "null" string).
I would like to remove these null fields, so I wrote this:
var l2:List[Rdv] = liste.list()
l2=l2.map( (w:Rdv) =>{
if ( w.telPrivé==null ) w.copy( telPrivé = "" )
})
but I get this error:
found:List[Any], required:List[Rdv]
so after the map I added ".asInstanceOf[List[Rdv]]" but then I get this error:
java.lang.ClassCastException: scala.runtime.BoxedUnit cannot be cast to metier.Objets$Rdv
It seems to ba a basic question, but I can't do that.
olivier.
Try this:
var l2: List[Rdv] = liste.list()
l2 = l2 map ((w: Rdv => if (w.telPrivé == null) w.copy( telPrivé = "" ) else w)
Could you try doing something like this?
val l2: List[Rdv] = liste list ()
val l3 = ls map{
case x # Rdv(_, null, _) => x.copy(telPrive = "")
case x => x
}
Honestly, should should make that field, if it's nullable to be an Option and then have a member function which you call defined such that:
case class Rdv(a: String, b: Option[String], c: String){
def realC = b getOrElse ""
}
Related
I'm fresh with scala and udf, now I would like to write a udf which accept 3 parameters from a dataframe columns(one of them is array), for..loop current array, parse and return a case class which will be used afterwards. here's a my code roughly:
case class NewFeatures(dd: Boolean, zz: String)
val resultUdf = udf((arrays: Option[Row], jsonData: String, placement: Int) => {
for (item <- arrays) {
val aa = item.getAs[Long]("aa")
val bb = item.getAs[Long]("bb")
breakable {
if (aa <= 0 || bb <= 0) break
}
val cc = item.getAs[Long]("cc")
val dd = cc > 0
val jsonData = item.getAs[String]("json_data")
val jsonDataObject = JSON.parseFull(jsonData).asInstanceOf[Map[String, Any]]
var zz = jsonDataObject.getOrElse("zz", "").toString
NewFeatures(dd, zz)
}
})
when I run it, it will get exception:
java.lang.UnsupportedOperationException: Schema for type Unit is not supported
how should I modify above udf
First of all, try better naming for your variables, for instance in your case, "arrays" is of type Option[Row]. Here, for (item <- arrays) {...} is basically a .map method, using map on Options, you should provide a function, that uses Row and returns a value of some type (~= signature: def map[V](f: Row => V): Option[V], what you want in your case: def map(f: Row => NewFeatures): Option[NewFeature]). While you're breaking out of this map in some circumstances, so there's no assurance for the compiler that the function inside map method would always return an instance of NewFeatures. So it is Unit (it only returns on some cases, and not all).
What you want to do could be enhanced in something similar to this:
val funcName: (Option[Row], String, Int) => Option[NewFeatures] =
(rowOpt, jsonData, placement) => rowOpt.filter(
/* your break condition */
).map { row => // if passes the filter predicate =>
// fetch data from row, create new instance
}
Given a sequence of Price objects, I want to map it to applyPromo function if a condition, i.e. promo == "FOO" applies, otherwise return the sequence as is.
This is my applyPromo:
val pricePromo = price => price.copy(amount = price.amount - someDiscount)
In a mutable way I probably would write it like this:
var prices: Seq[Price] = Seq(price1, price2, ...)
.map(doStuff)
.map(doSomeOtherStuff)
if (promo == "FOO") {
prices = prices.map(applyPromo)
}
prices
I was wondering if I could do something similar like this while keeping the immutable approach of scala. Instead of creating a temp var, I prefer to keep the chain.
Pseudo-code:
val prices = Seq(price1, price2, ...)
prices
.map(dosStuff)
.map(doOtherStuff)
.mapIf(promo == "FOO", applyPromo)
I don't want to check the condition within the map function in this case, as it applies for all elements:
prices.map(price => {
if (promo == "FOO") {
applyDiscount(price)
} else
price
}
)
You just need to use else to make it functional (and you can create an implicit class to add the mapIf method if you prefer):
val prices: Seq[Price] = Seq(price1, price2,...).map(doStuff).map(doSomeOtherStuff)
/* val resultPrices = */ if (promo == "FOO") {
prices.map(price => {
price.copy(amount = price.amount - someDiscount)
})
} else prices
Something like this:
implicit class ConditionalMap[T](seq: Seq[T]) extends AnyVal {
def mapIf[Q](cond: =>Boolean, f: T => Q): Seq[Q] = if (cond) seq.map(f) else seq
}
You can also map(x => x) in the else case:
val discountFunction = if (promo == "FOO") (price: Price) =>
price.copy(amount = price.amount - someDiscount) else (x: Price) => x
val prices: Seq[Price] = Seq(price1, price2,...).
map(doStuff).
map(doSomeOtherStuff).
map(discountFunction)
I'd do it like this:
val maybePromo: (Price => Price) =
if(promo == "FOO") applyPromo else identity _
prices.map(maybePromo)
Or you can inline it within map itself:
prices.map(if(promo == "FOO") applyPromo else identity)
In scalaz, a function A => A is called an endomorphism and is a Monoid whose associative binary operation is function composition and whose identity is the identity function. This is useful because there is a bunch of syntax available where monoids are concerned. For example, scalaz adds the ?? operation to boolean along these lines:
def ??[A: Monoid](a: A) = if (self) a else Monoid[A].zero
Thus:
prices
.map(doStuff)
.map(doSomeOtherStuff)
.map(((promo === "FOO") ?? deductDiscount).run)
Where:
val deductDiscount: Endo[Price] = Endo(px => px.copy(amount = px.amount - someDiscount))
The above all requires
import scalaz._
import Scalaz._
Notes
=== is typesafe equals syntax
?? is boolean syntax
oxbow_lakes has an interesting answer
Easy way solve to me is wrapping Seq in a Option context.
scala> case class Price(amount: Double)
defined class Price
when condition matches,
scala> val promo = "FOO"
promo: String = FOO
scala> Some(Seq(Price(1), Price(2), Price(3))).collect{
case prices if promo == "FOO" => prices.map { p => p.copy(p.amount - 1 )}
case prices => prices}
res6: Option[Seq[Price]] = Some(List(Price(0.0), Price(1.0), Price(2.0)))
when condition does not match
scala> val promo = "NOT-FOO"
promo: String = NOT-FOO
scala> Some(Seq(Price(1), Price(2), Price(3))).collect{
case prices if promo == "FOO" => prices.map { p => p.copy(p.amount - 1 )}
case prices => prices}
res7: Option[Seq[Price]] = Some(List(Price(1.0), Price(2.0), Price(3.0)))
I'm trying to write a function that returns a list (for querying purposes) that has some wildcard elements:
def createPattern(query: List[(String,String)]) = {
val l = List[(_,_,_,_,_,_,_)]
var iter = query
while(iter != null) {
val x = iter.head._1 match {
case "userId" => 0
case "userName" => 1
case "email" => 2
case "userPassword" => 3
case "creationDate" => 4
case "lastLoginDate" => 5
case "removed" => 6
}
l(x) = iter.head._2
iter = iter.tail
}
l
}
So, the user enters some query terms as a list. The function parses through these terms and inserts them into val l. The fields that the user doesn't specify are entered as wildcards.
Val l is causing me troubles. Am I going the right route or are there better ways to do this?
Thanks!
Gosh, where to start. I'd begin by getting an IDE (IntelliJ / Eclipse) which will tell you when you're writing nonsense and why.
Read up on how List works. It's an immutable linked list so your attempts to update by index are very misguided.
Don't use tuples - use case classes.
You shouldn't ever need to use null and I guess here you mean Nil.
Don't use var and while - use for-expression, or the relevant higher-order functions foreach, map etc.
Your code doesn't make much sense as it is, but it seems you're trying to return a 7-element list with the second element of each tuple in the input list mapped via a lookup to position in the output list.
To improve it... don't do that. What you're doing (as programmers have done since arrays were invented) is to use the index as a crude proxy for a Map from Int to whatever. What you want is an actual Map. I don't know what you want to do with it, but wouldn't it be nicer if it were from these key strings themselves, rather than by a number? If so, you can simplify your whole method to
def createPattern(query: List[(String,String)]) = query.toMap
at which point you should realise you probably don't need the method at all, since you can just use toMap at the call site.
If you insist on using an Int index, you could write
def createPattern(query: List[(String,String)]) = {
def intVal(x: String) = x match {
case "userId" => 0
case "userName" => 1
case "email" => 2
case "userPassword" => 3
case "creationDate" => 4
case "lastLoginDate" => 5
case "removed" => 6
}
val tuples = for ((key, value) <- query) yield (intVal(key), value)
tuples.toMap
}
Not sure what you want to do with the resulting list, but you can't create a List of wildcards like that.
What do you want to do with the resulting list, and what type should it be?
Here's how you might build something if you wanted the result to be a List[String], and if you wanted wildcards to be "*":
def createPattern(query:List[(String,String)]) = {
val wildcard = "*"
def orElseWildcard(key:String) = query.find(_._1 == key).getOrElse("",wildcard)._2
orElseWildcard("userID") ::
orElseWildcard("userName") ::
orElseWildcard("email") ::
orElseWildcard("userPassword") ::
orElseWildcard("creationDate") ::
orElseWildcard("lastLoginDate") ::
orElseWildcard("removed") ::
Nil
}
You're not using List, Tuple, iterator, or wild-cards correctly.
I'd take a different approach - maybe something like this:
case class Pattern ( valueMap:Map[String,String] ) {
def this( valueList:List[(String,String)] ) = this( valueList.toMap )
val Seq(
userId,userName,email,userPassword,creationDate,
lastLoginDate,removed
):Seq[Option[String]] = Seq( "userId", "userName",
"email", "userPassword", "creationDate", "lastLoginDate",
"removed" ).map( valueMap.get(_) )
}
Then you can do something like this:
scala> val pattern = new Pattern( List( "userId" -> "Fred" ) )
pattern: Pattern = Pattern(Map(userId -> Fred))
scala> pattern.email
res2: Option[String] = None
scala> pattern.userId
res3: Option[String] = Some(Fred)
, or just use the map directly.
I want to check if the string contains the character. I am writing a hangman code.
For example, here is the word to guess: "scala", but it looks like "_ _ _ _ _" tho the user. Let's assume that user inputs letter 'a', then it must look like "_ _ a _ a".
def checkGuess(){
if (result.contains(user_input)) {
val comp = result.toCharArray
for (i <- comp){
if (user_input != comp(i))
comp(i) = '_'
comp(i)
}
val str = comp.toString
}
}
Is this right?
Thank you in advance.
I don't think this is homework, so I'll probably regret answering if it is...
case class HangmanGame(goal: String, guesses: Set[Char] = Set.empty[Char]) {
override def toString = goal map {c => if (guesses contains c) c else '_'} mkString " "
val isComplete = goal forall { guesses.contains }
def withGuess(c: Char) = copy(guesses = guesses + c)
}
Then
val h = HangmanGame("scala")
h: HangmanGame = _ _ _ _ _
scala> val h1 = h.withGuess('a')
h1: HangmanGame = _ _ a _ a
scala> val h2 = h1.withGuess('l')
h2: HangmanGame = _ _ a l a
scala> val h3 = h2.withGuess('s')
h3: HangmanGame = s _ a l a
scala> val h4 = h3.withGuess('c')
h4: HangmanGame = s c a l a
scala> h4.isComplete
res5: Boolean = true
UPDATE
Okay, so it does look like homework. I guess the genie's out of the bottle now, but unless you get up to speed on Scala very quickly you're going to have a really hard time explaining how it works.
How about:
scala> def checkGuess(str: String, c: Char) = str.replaceAll("[^"+c+"]","_")
checkGuess: (str: String,c: Char)java.lang.String
scala> checkGuess("scala",'a')
res1: java.lang.String = __a_a
scala> def checkGuess2(str: String, C: Char) = str map { case C => C; case _ => '_'}
checkGuess2: (str: String,C: Char)String
scala> checkGuess2("scala",'a')
res2: String = __a_a
Here are some comments about how you wrote this. When using this syntax, def checkGuess() { ... }, the function will not return any value, it will return Unit instead.
This means that you're using it for its side effect only (such as setting some var outside the code block or printing some values). The issue is that you are not setting any value or printing anything inside the function (no printing, no assignment).
What you don't show in your code snippet is where you store the string to guess, the user input and the feedback to print. You can pass the first two as arguments and the last one as a returned value. This make the input and output self contained in the function and does not presume where you render the feedback.
def feedback(target:String, guesses:String): String = {
// target is the string to guess like "scala"
// guesses are the letters that have been provided so far, like "ac"
// last expression should be the feedback to print for instance "_ca_a"
}
Then you can think about the function as transforming each letter in target with _ or with itself depending on whether it is contained in guesses. For this the target map { c => expr } would work pretty well if you figure out how to make expr return c if c is in guesses and '_' otherwise.
Staying as close as possible to the main question ( How to check if a character is contained in string? ) what I did was changing the approach, i.e.:
Inside a for loop, I wanted to do something like some_chr == 't'
and I did the following some_chr.toString == "t" and it worked just fine.
For example, from a following file:
Name,Surname,E-mail
John,Smith,john.smith#hotmail.com
Nancy,Smith,nancy.smith#gmail.com
Jane,Doe,jane.doe#aol.com
John,Doe,john.doe#yahoo.com
how do I get e-mail address of John Doe?
I use the following code now, but can specify only one key field now:
val src = Source.fromFile(file)
val iter = src.getLines().drop(1).map(_.split(","))
var quote = ""
iter.find( _(1) == "Doe" ) foreach (a => println(a(2)))
src.close()
I've tried writing "iter.find( _(0) == "John" && _(1) == "Doe" )", but this raises an error saying that only one parameter is expected (enclosing the condition into extra pair of parentheses does not help).
The underscore as a placeholder for a parameter to a lambda doesn't work the way that you think.
a => println(a)
// is equivalent to
println(_)
(a,b) => a + b
// is equivalent to
_ + _
a => a + a
// is not equivalent to
_ + _
That is, the first underscore means the first parameter and the second one means the second parameter and so on. So that's the reason for the error that you're seeing -- you're using two underscores but have only one parameter. The fix is to use the explicit version:
iter.find( a=> a(0) == "John" && a(1) == "Doe" )
You can use Regex:
scala> def getRegex(v1: String, v2: String) = (v1 + "," + v2 +",(\\S+)").r
getRegex: (v1: String,v2: String)scala.util.matching.Regex
scala> val src = """John,Smith,john.smith#hotmail.com
| Nancy,Smith,nancy.smith#gmail.com
| Jane,Doe,jane.doe#aol.com
| John,Doe,john.doe#yahoo.com
| """
src: java.lang.String =
John,Smith,john.smith#hotmail.com
Nancy,Smith,nancy.smith#gmail.com
Jane,Doe,jane.doe#aol.com
John,Doe,john.doe#yahoo.com
scala> val MAIL = getRegex("John","Doe")
MAIL: scala.util.matching.Regex = John,Doe,(\S+)
scala> val itr = src.lines
itr: Iterator[String] = non-empty iterator
scala> for(MAIL(address) <- itr) println(address)
john.doe#yahoo.com
scala>
You could also do a pattern match on the result of split in a for comprehension.
val firstName = "John"
val surName = "Doe"
val emails = for {
Array(`firstName`, `surName`, email) <-
src.getLines().drop(1) map { _ split ',' }
} yield { email }
println(emails.mkString(","))
Note the backticks in the pattern: this means we match on the value of firstName instead of introducing a new variable matching anything and shadowing the val firstname.