I want to find if the specific string is present in the list for example
val fruit: List[String] = List("apples", "oranges", "pears")
I want to check if oranges is present in the given list
It would be great if someone can help me on this. TIA
there are several ways to do that:
scala> val fruits: List[String] = List("apples", "oranges", "pears")
fruits: List[String] = List(apples, oranges, pears)
using .contains
scala> val hasApples = fruit.contains("apples")
hasApples: Boolean = true
scala> val hasBananas = fruit.contains("bananas")
bananas: Boolean = false
or using .find
scala> fruits.find(_ == "apples")
res1: Option[String] = Some(apples)
scala> fruits.find(_ == "bananas")
res2: Option[String] = None
check the documentation for other useful methods on: http://www.scala-lang.org/api/current/#scala.collection.immutable.List
Related
How can I write an expression to filter inputs so that it would be in the format of
(AAA) where A is a number from 0-9.
EX: (123), (592), (999)
Usually you want to do more than filter.
scala> val r = raw"\(\d{3}\)".r
r: scala.util.matching.Regex = \(\d{3}\)
scala> List("(123)", "xyz", "(456)").filter { case r() => true case _ => false }
res0: List[String] = List((123), (456))
scala> import PartialFunction.{cond => when}
import PartialFunction.{cond=>when}
scala> List("(123)", "xyz", "(456)").filter(when(_) { case r() => true })
res1: List[String] = List((123), (456))
Keeping all matches from each input:
scala> List("a(123)b", "xyz", "c(456)d").flatMap(s =>
| r.findAllMatchIn(s).map(_.matched).toList)
res2: List[String] = List((123), (456))
scala> List("a(123)b", "xyz", "c(456)d(789)e").flatMap(s =>
| r.findAllMatchIn(s).map(_.matched).toList)
res3: List[String] = List((123), (456), (789))
Keeping just the first:
scala> val r = raw"(\(\d{3}\))".r.unanchored
r: scala.util.matching.UnanchoredRegex = (\(\d{3}\))
scala> List("a(123)b", "xyz", "c(456)d(789)e").flatMap(r.unapplySeq(_: String)).flatten
res4: List[String] = List((123), (456))
scala> List("a(123)b", "xyz", "c(456)d(789)e").collect { case r(x) => x }
res5: List[String] = List((123), (456))
Keeping entire lines that match:
scala> List("a(123)b", "xyz", "c(456)d(789)e").collect { case s # r(_*) => s }
res6: List[String] = List(a(123)b, c(456)d(789)e)
Java API:
scala> import java.util.regex._
import java.util.regex._
scala> val p = Pattern.compile(raw"(\(\d{3}\))")
p: java.util.regex.Pattern = (\(\d{3}\))
scala> val q = p.asPredicate
q: java.util.function.Predicate[String] = java.util.regex.Pattern$$Lambda$1107/824691524#3234474
scala> List("(123)", "xyz", "(456)").filter(q.test)
res0: List[String] = List((123), (456))
Typically you create regexes by using the .r method available on strings, such as "[0-9]".r. However, as you have noticed, that means you can't interpolate escape characters, as the parser thinks you want to insert escape characters into the string, not the regex.
For this, you can use Scala's triple-quoted strings, which create strings of the exact character sequence, including backslashes and newlines.
To create a regex like you describe, you could write """\(\d\d\d\)""".r. Here's an example of it in use:
val regex = """\(\d\d\d\)""".r.pattern
Seq("(123)", "(---)", "456").filter(str => regex.matcher(str).matches)
I have a 2 list of following class
case class User(var userId: Int =0,
var userName: String ="",
var email: String="",
var password: String ="") {
def this() = this(0, "", "", "")
}
globalList of User class.
localList of User class.
I would like to remove/filter all items from globalList that are same userId in localList.
I tried couple of api with no success such as filterNot, filter, drop, dropWhile. Please advice me how it can be done.
The diff operator "Computes the multiset difference between this list and another sequence".
scala> val global = List(0,1,2,3,4,5)
global: List[Int] = List(0, 1, 2, 3, 4, 5)
scala> val local = List(1,2,3)
local: List[Int] = List(1, 2, 3)
scala> global.diff(local)
res9: List[Int] = List(0, 4, 5)
You can try the following:
val userIdSet = localList.map(_.userId).toSet
val filteredList = globalList.filterNot(u => userIdSet.contains(u.userId))
I expect regex "[a-zA-Z]\\d{6}" to match "z999999" but it is not matching as an empty List is mapped :
val lines = List("z999999"); //> lines : List[String] = List(z999999)
val regex = """[a-zA-Z]\d{6}""".r //> regex : scala.util.matching.Regex = [a-zA-Z]\d{6}
val fi = lines.map(line => line match { case regex(group) => group case _ => "" })
//> fi : List[String] = List("")
Is there a problem with my regex or how I'm using it with Scala ?
val l="z999999"
val regex = """[a-zA-Z]\d{6}""".r
regex.findAllIn(l).toList
res1: List[String] = List(z999999)
The regex seems valid.
lines.map( _ match { case regex(group) => group; case _ => "" })
res2: List[String] = List("")
How odd. Let's see what happens with a capturing group around the whole expression we defined in regex.
val regex2= """([a-zA-Z]\d{6})""".r
regex2: scala.util.matching.Regex = ([a-zA-Z]\d{6})
lines.map( _ match { case regex2(group) => group; case _ => "" })
res3: List[String] = List(z999999)
Huzzah.
The unapply method on a regex is for getting the results of capturing groups.
There are other methods on a regex object that just get matches (e.g. findAllIn, findFirstIn, etc)
I have following list structure -
"disks" : [
{
"name" : "A",
"memberNo" :1
},
{
"name" : "B",
"memberNo" :2
},
{
"name" : "C",
"memberNo" :3
},
{
"name" : "D",
}
]
I have many elements in list and want to check for 'memberNo', if it exists
I want count of from list elements.
e.g. here count will be 3
How do I check if key exists and get count of elements from list using scala??
First create class to represent your input data
case class Disk (name : String, memberNo : String)
Next load data from repository (or other datasource)
val disks: List[Disk] = ...
And finally count
disks.count(d => Option(d.memberNo).isDefined)
In a similar fashion as in #SergeyLagutin answer, consider this case class
case class Disk (name: String, memberNo: Option[Int] = None)
where missing memberNo are defaulted with None; and this list,
val disks = List( Disk("A", Some(1)),
Disk("B", Some(2)),
Disk("C", Some(3)),
Disk("D"))
Then with flatMap we can filter out those disks with some memberNo, as follows,
disks.flatMap(_.memberNo)
res: List[Int] = List(1, 2, 3)
Namely, for the counting,
disks.flatMap(_.memberNo).size
res: Int = 3
Likewise, with a for comprehension,
for (d <- disks ; m <- d.memberNo) yield m
res: List[Int] = List(1, 2, 3)
What is the problem with parsing the blank/whitespace?
scala> object BlankParser extends RegexParsers {
def blank: Parser[Any] = " "
def foo: Parser[Any] = "foo"
}
defined module BlankParser
scala> BlankParser.parseAll(BlankParser.foo, "foo")
res15: BlankParser.ParseResult[Any] = [1.4] parsed: foo
scala> BlankParser.parseAll(BlankParser.blank, " ")
res16: BlankParser.ParseResult[Any] =
[1.2] failure: ` ' expected but ` ' found
^
scala>
the lexer for scala throws blankspaces away.
try
override val skipWhitespace = false
to avoid this.
the question was already solved so it seems...
Scala parser combinators for language embedded in html or text (like php)