The Scala filter Method
Notes:
filterloops over a sequence- It’s like a basic
for/yieldexpression with a guard
- It’s like a basic
filteronly returns elements that match the filtering expression- think "retain"
filtertakes a function as an argument- the function (algorithm) you supply should work on a single element and return a
Booleanvalue (i.e., your function is a predicate) - your function’s input parameter type must match the type in the collection
- ex: if it’s a
List[Int], your algorithm should take anIntand return aBoolean
- ex: if it’s a
- the function (algorithm) you supply should work on a single element and return a
filter examples
Some filter examples:
val xs = (1 to 10).toList
// filter examples
val smalls = xs.filter(x => x < 5)
val smalls = xs.filter(_ < 5)
val larges = xs.filter(_ > 5)
val oops = xs.filter(_ > 100) // List()filter is like this much longer for expression:
val ys =
for
x <- xs
if x > 5
yield
xMore examples
val fruits = Seq("orange", "peach", "apple", "banana")
val as = fruits.filter(fruit => fruit.startsWith("a")) // long
val as = fruits.filter(_.startsWith("a")) // short
val longNames = fruits.filter(_.length > 5)Using a function with filter
// a List
val list = "apple" :: "banana" :: 1 :: 2.2 :: Nil
// a function (predicate) that works on any Matchable
def onlyStrings(a: Matchable): Boolean = a match
case s: String => true
case _ => false
// use the function with the List and filter
val strings = list.filter(onlyStrings) // List("apple", "banana")filter and filterNot
val a = (0 to 100 by 10).toVector
a.filter(_ < 20) // Vector(0, 10)
a.filter(_ > 1_000) // Vector()
a.filterNot(_ < 45) // Vector(50, 60, 70, 80, 90, 100)
