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Scala Set (collection)

Scala collections Scala collections

Scala Set (collection) is not repeated collection of objects, all elements are unique.

Scala collection is divided into variable and immutable collections.

By default, Scala using immutable collections, if you want to use the variable set, you need to referencescala.collection.mutable.Set package.

The default reference scala.collection.immutable.Set, immutable set of examples are as follows: 

val set = Set(1,2,3)
println(set.getClass.getName) // 

println(set.exists(_ % 2 == 0)) //true
println(set.drop(1)) //Set(2,3)

If you need to use a variable collection need to introduce scala.collection.mutable.Set: 

import scala.collection.mutable.Set // 可以在任何地方引入 可变集合

val mutableSet = Set(1,2,3)
println(mutableSet.getClass.getName) // scala.collection.mutable.HashSet

mutableSet.add(4)
mutableSet.remove(1)
mutableSet += 5
mutableSet -= 2

println(mutableSet) // Set(5, 3, 4)

val another = mutableSet.toSet
println(another.getClass.getName) // scala.collection.immutable.Set

Note: Although variable and immutable Set Set has add or delete elements, but there is a very big difference.An immutable Set operation, will produce a new set, the original set has not changed, which is the same as List. The operation of the variable Set change is that the Set itself, similar to ListBuffer.

Collection of basic operations

Scala collection has three basic operations:

  • head returns the first element of the collection
  • tail returns a collection that contains in addition to the other elements of the first element
  • isEmpty returns true if the collection is empty

Any operation for Scala collections can be used to express the three basic operations. Examples are as follows: 

object Test {
   def main(args: Array[String]) {
      val site = Set("w3big", "Google", "Baidu")
      val nums: Set[Int] = Set()

      println( "第一网站是 : " + site.head )
      println( "最后一个网站是 : " + site.tail )
      println( "查看列表 site 是否为空 : " + site.isEmpty )
      println( "查看 nums 是否为空 : " + nums.isEmpty )
   }
}

Implementation of the above code, the output is: 

$ vim Test.scala 
$ scala Test.scala 
第一网站是 : w3big
最后一个网站是 : Set(Google, Baidu)
查看列表 site 是否为空 : false
查看 nums 是否为空 : true

Connection set

You can use the++ operator or Set. ++ ()Method to connect two sets. If there are duplicate elements will remove duplicate elements. Examples are as follows: 

object Test {
   def main(args: Array[String]) {
      val site1 = Set("w3big", "Google", "Baidu")
      val site2 = Set("Faceboook", "Taobao")

      // ++ 作为运算符使用
      var site = site1 ++ site2
      println( "site1 ++ site2 : " + site )

      //  ++ 作为方法使用
      site = site1.++(site2)
      println( "site1.++(site2) : " + site )
   }
}

Implementation of the above code, the output is: 

$ vim Test.scala 
$ scala Test.scala 
site1 ++ site2 : Set(Faceboook, Taobao, Google, Baidu, w3big)
site1.++(site2) : Set(Faceboook, Taobao, Google, Baidu, w3big)

Find the maximum and minimum elements in the collection

You can useSet.min method to find the smallest element in the collection, use Set.maxway to find the largest element in the collection. Examples are as follows: 

object Test {
   def main(args: Array[String]) {
      val num = Set(5,6,9,20,30,45)

      // 查找集合中最大与最小元素
      println( "Set(5,6,9,20,30,45) 集合中的最小元素是 : " + num.min )
      println( "Set(5,6,9,20,30,45) 集合中的最大元素是 : " + num.max )
   }
}

Implementation of the above code, the output is: 

$ vim Test.scala 
$ scala Test.scala 
Set(5,6,9,20,30,45) 集合中的最小元素是 : 5
Set(5,6,9,20,30,45) 集合中的最大元素是 : 45

Intersection

You can use theSet. & Set.intersectmethod or methods to see the intersection of the two sets of elements. Examples are as follows: 

object Test {
   def main(args: Array[String]) {
      val num1 = Set(5,6,9,20,30,45)
      val num2 = Set(50,60,9,20,35,55)

      // 交集
      println( "num1.&(num2) : " + num1.&(num2) )
      println( "num1.intersect(num2) : " + num1.intersect(num2) )
   }
}

Implementation of the above code, the output is: 

$ vim Test.scala 
$ scala Test.scala 
num1.&(num2) : Set(20, 9)
num1.intersect(num2) : Set(20, 9)

Scala Set common method

The following table lists the Scala Set commonly used methods:

No. Method and Description
1

def + (elem: A): Set [A]

Add a new element to the collection, x and create a new collection, unless the existing elements

2

def - (elem: A): Set [A]

Removing elements of the collection, and create a new collection

3

def contains (elem: A): Boolean

If the element is present in the collection, it returns true, otherwise returns false.

4

def & (that: Set [A ]): Set [A]

Returns the intersection of two sets

5

def & ~ (that: Set [ A]): Set [A]

Returns the set difference of two sets

6

def + (elem1: A, elem2 : A, elems: A *): Set [A]

By adding incoming elements of the specified collection to create a new set of immutable

7

def ++ (elems: A): Set [A]

Merging two collections

8

def - (elem1: A, elem2 : A, elems: A *): Set [A]

By removing the elements of the specified collection passed to create a new set of immutable

9

def addString (b: StringBuilder): StringBuilder

Add all the elements of the collection to the immutable string buffer

10

def addString (b: StringBuilder, sep : String): StringBuilder

Add all the elements of an immutable collection into a string buffer, using the specified delimiter

11

def apply (elem: A)

Detecting whether the collection contains the specified element

12

def count (p: (A) => Boolean): Int

Calculate the number of elements that meet the specified criteria set

13

def copyToArray (xs: Array [A ], start: Int, len: Int): Unit

Copy immutable collection element to an array

14

def diff (that: Set [A ]): Set [A]

Difference sets comparing two sets

15

def drop (n: Int): Set [A]]

The new collection before returning discards n elements

16

def dropRight (n: Int): Set [A]

Back discard the last n elements of the new collection

17

def dropWhile (p: (A) => Boolean): Set [A]

Discard element left to right, until the condition is not satisfied p

18

def equals (that: Any): Boolean

equals method can be used in any sequence. For comparing the series are equal.

19

def exists (p: (A) => Boolean): Boolean

Analyzing immutable set the conditions specified element exists.

20

def filter (p: (A) => Boolean): Set [A]

Output meets all specified criteria immutable collection elements.

twenty one

def find (p: (A) => Boolean): Option [A]

Finding the first element in the collection immutable meet the specified criteria

twenty two

def forall (p: (A) => Boolean): Boolean

Find all the elements of an immutable collection that meets the specified criteria

twenty three

def foreach (f: (A) => Unit): Unit

The function is applied to all elements of the immutable collection

twenty four

def head: A

Get the first element of the collection immutable

25

def init: Set [A]

Returns all elements, except the last one

26

def intersect (that: Set [A ]): Set [A]

Compute the intersection of two sets

27

def isEmpty: Boolean

Determine whether the collection is empty

28

def iterator: Iterator [A]

Create a new iterator to iterate the elements

29

def last: A

Returns the last element

30

def map [B] (f: (A) => B): immutable.Set [B]

Through a given method will recalculate all the elements

31

def max: A

Find the maximum element

32

def min: A

Find the smallest element

33

def mkString: String

The set of all elements of the display as a string

34

def mkString (sep: String): String

Separators will bring together all the elements displayed as a string

35

def product: A

Returns an immutable set of numbers in the plot elements.

36

def size: Int

Returns the number of elements in the collection immutable

37

def splitAt (n: Int): (Set [A], Set [A])

The immutable collection is split into two containers, the first by the first n elements, and the second by the remaining elements

38

def subsetOf (that: Set [A ]): Boolean

If the collection contains a subset returns true, false otherwise

39

def sum: A

Returns an immutable set of all elements of the digital and

40

def tail: Set [A]

Returns an immutable set of other elements in addition to the first element

41

def take (n: Int): Set [A]

Returns the first n elements

42

def takeRight (n: Int): Set [A]

n elements Back

43

def toArray: Array [A]

Will be converted to a digital collection

44

def toBuffer [B>: A] : Buffer [B]

Back buffer, contains all the elements of a collection of immutable

45

def toList: List [A]

Back List, contains all the elements of a collection of immutable

46

def toMap [T, U]: Map [T, U]

Back Map, contains all the elements of a collection of immutable

47

def toSeq: Seq [A]

Back Seq, contains all the elements of a collection of immutable

48

def toString (): String

Returns a string to object to represent

More ways to refer to the API documentation

Scala collections Scala collections