Scala数组和集合

时间：2023-03-09 08:09:36
Scala数组和集合

一、scala数组

    数组定义1： var arr = new Array[String](3)

    String:存储的元素类型

    3:存储3个元素

    添加元素： arr(1) = "hello"

    数组定义2： val arr1 = Array[Int](1,2,3,4,5,6)

    改变内容：arr1(1) = 18

    添加元素：arr1 += 22 长度不可以改变

二、数组方法

1、map（映射）

    映射： 2 4 6

    映射关系：f(x) = x*5

    对应映射关系：10 20 30

例：

scala> var arr = Array(1,2,3)

arr: Array[Int] = Array(1, 2, 3)

scala> arr.map((x: Int) => x * 10)

res12: Array[Int] = Array(10, 20, 30)

scala> arr

res13: Array[Int] = Array(1, 2, 3)

scala> res12

res14: Array[Int] = Array(10, 20, 30)

2、flatten（扁平化操作）

scala> var arr = Array("hello Beijing","hello China")

arr: Array[String] = Array(hello Beijing, hello China)

scala> arr.length

res6: Int = 2

scala> arr.map(_.split(" "))

res7: Array[Array[String]] = Array(Array(hello, Beijing), Array(hello, China))

scala> arr.map(_.split(" ")).flatten

res8: Array[String] = Array(hello, Beijing, hello, China)

3、flatMap（相当于先map操作再flatten）

scala> arr

res9: Array[String] = Array(hello Beijing, hello China)

scala> arr.flatMap(_.split(" "))

res10: Array[String] = Array(hello, Beijing, hello, China)

4、foreach（遍历数组中的元素）

scala> res10.foreach(x => println(x))

hello

Beijing

hello

China

scala>

5、GroupBy（分组）

scala> arr

res13: Array[String] = Array(hello Beijing, hello China)

scala> arr.flatMap(_.split(" ")).groupBy(x => x)

res14: scala.collection.immutable.Map[String,Array[String]] = Map(Beijing -> Array(Beijing), China -> Array(China), hello -> Array(hello, hello))

//Scala简易WordCount

scala> arr.flatMap(_.split(" ")).groupBy(x => x).map(x => (x._1,x._2.length))

res16: scala.collection.immutable.Map[String,Int] = Map(Beijing -> 1, China -> 1, hello -> 2)

6、sortBy（排序）

scala> arr

res13: Array[String] = Array(hello Beijing, hello China)

//正序

scala> arr.flatMap(_.split(" ")).groupBy(x => x).map(x => (x._1,x._2.length)).toList.sortBy(x => x._2)

res18: List[(String, Int)] = List((Beijing,1), (China,1), (hello,2))

//倒序

scala> arr.flatMap(_.split(" ")).groupBy(x => x).map(x => (x._1,x._2.length)).toList.sortBy(x => -x._2)

res19: List[(String, Int)] = List((hello,2), (Beijing,1), (China,1))

三、集合

    scala集合有两种类型：可变mutable

    不可变Immutable

    val b = List(2,4,6)

    不可变集合：内容不可变（数组内容可改变）

    长度不可变

    可变集合：

    注意：需要导包

    import scala.collection.mutable._

    val buff = ArrayBuffer(2,3,4)

    内容可变: buff(1) = 300

    长度可变：buff += 200

例：

scala> val s = List(1,2,3)

s: List[Int] = List(1, 2, 3)

scala> s(1) = 8

<console>:13: error: value update is not a member of List[Int]

       s(1) = 8

       ^

scala> val b = List(2,3,4)

b: List[Int] = List(2, 3, 4)

scala> b += 20

<console>:13: error: value += is not a member of List[Int]

       b += 20

         ^

scala> import scala.collection.mutable._

import scala.collection.mutable._

scala> val buff = ArrayBuffer(2,3,4)

buff: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(2, 3, 4)

scala> buff += 200

res23: buff.type = ArrayBuffer(2, 3, 4, 200)

scala> buff(1) = 300

scala> buff

res25: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(2, 300, 4, 200)

scala> scala.collection.mutable.

AVLIterator            History               PriorityQueueProxy

AVLTree                ImmutableMapAdaptor   Publisher

AbstractBuffer         ImmutableSetAdaptor   Queue

AbstractIterable       IndexedSeq            QueueProxy

AbstractMap            IndexedSeqLike        ResizableArray

AbstractSeq            IndexedSeqOptimized   RevertibleHistory

AbstractSet            IndexedSeqView        Seq

AnyRefMap              Iterable              SeqLike

ArrayBuffer            LazyBuilder           Set

ArrayBuilder           Leaf                  SetBuilder

ArrayLike              LinearSeq             SetLike

ArrayOps               LinkedEntry           SetProxy

ArraySeq               LinkedHashMap         SortedSet

ArrayStack             LinkedHashSet         Stack

BitSet                 LinkedList            StackProxy

Buffer                 LinkedListLike        StringBuilder

BufferLike             ListBuffer            Subscriber

BufferProxy            ListMap               SynchronizedBuffer

Builder                LongMap               SynchronizedMap

Cloneable              Map                   SynchronizedPriorityQueue

DefaultEntry           MapBuilder            SynchronizedQueue

DefaultMapModel        MapLike               SynchronizedSet

DoubleLinkedList       MapProxy              SynchronizedStack

DoubleLinkedListLike   MultiMap              Traversable

FlatHashTable          MutableList           TreeSet

GrowingBuilder         ObservableBuffer      Undoable

HashEntry              ObservableMap         UnrolledBuffer

HashMap                ObservableSet         WeakHashMap

HashSet                OpenHashMap           WrappedArray

HashTable              PriorityQueue         WrappedArrayBuilder

scala> val lb = scala.collection.mutable.ListBuffer(11,22,33)

lb: scala.collection.mutable.ListBuffer[Int] = ListBuffer(11, 22, 33)

scala> lb(1) = 334

scala> lb += 222

res27: lb.type = ListBuffer(11, 334, 33, 222)

scala> lb

res28: scala.collection.mutable.ListBuffer[Int] = ListBuffer(11, 334, 33, 222)

四、长度可变的数组

    创建长度可变数组：

    val ab = scala.collection.mutable.ArrayBuffer(2,3,4)

    长度可变：

    ab += 440

五、Seq序列

    不可变的序列

    在scala中列表要么为空（Nil表示空列表）

    head元素上加上一个tail列表

    head:取头元素

    tail:取尾元素（除了头全是尾）

    5::Nil 空列表的头加入一个元素

    1::2::3::Nil 空列表前加入三个元素1,2,3

    + 字符串的拼接

    ++ 两个集合相加

    ++: 合并集合

    .+: 头部追加元素

    :+ 尾部追加元素

    ::: 两个集合相加

    count 统计个数

    filter 过滤

    sortBy 排序

    sortWwith 排序

    grouped 分组

    fold 折叠

    foldLeft 左折叠

    foldRight 右折叠

    reduce 聚合

    aggregate 先局部聚合再全局聚合

    zip 拉链

    sum 求和

例：

scala> import scala.collection.immutable._

import scala.collection.immutable._

scala> Nil

res30: scala.collection.immutable.Nil.type = List()

scala> val l = List(2,1,5,8,9)

l: List[Int] = List(2, 1, 5, 8, 9)

scala> l.head

res31: Int = 2

scala> l.tail

res32: List[Int] = List(1, 5, 8, 9)

scala> 5::Nil

res33: List[Int] = List(5)

scala> val s = Nil

s: scala.collection.immutable.Nil.type = List()

scala> 3::s

res34: List[Int] = List(3)

scala> s

res35: scala.collection.immutable.Nil.type = List()

scala> res34

res36: List[Int] = List(3)

scala> 1::2::3::Nil

res37: List[Int] = List(1, 2, 3)

scala> val ll = List(3,4,5)

ll: List[Int] = List(3, 4, 5)

scala> ll + "a"

res38: String = List(3, 4, 5)a

scala> ll

res39: List[Int] = List(3, 4, 5)

scala> ll ++ List(6,7)

res40: List[Int] = List(3, 4, 5, 6, 7)

scala> ll ++:List(6,7,8)

res41: List[Int] = List(3, 4, 5, 6, 7, 8)

scala> ll

res42: List[Int] = List(3, 4, 5)

scala> ll.+:(55)

res43: List[Int] = List(55, 3, 4, 5)

scala> ll:+(66)

res44: List[Int] = List(3, 4, 5, 66)

scala> ll

res45: List[Int] = List(3, 4, 5)

scala> val lll = List(33,44)

lll: List[Int] = List(33, 44)

scala> ll::lll

res46: List[Any] = List(List(3, 4, 5), 33, 44)

scala> ll:::lll

res47: List[Int] = List(3, 4, 5, 33, 44)

scala> ll

res48: List[Int] = List(3, 4, 5)

scala> ll.count(x => x>4)

res49: Int = 1

scala> ll.count(x => x>=4)

res50: Int = 2

scala> ll.filter(x => x >+5)

<console>:19: error: value >+ is not a member of Int

       ll.filter(x => x >+5)

                        ^

scala> ll.filter(x => x >=5)

res52: List[Int] = List(5)

scala> ll.filter(x => x >= 5)

res53: List[Int] = List(5)

scala> val ls = List(6,2,1,3,8,7)

ls: List[Int] = List(6, 2, 1, 3, 8, 7)

scala> ls.sortBy(x => x)

res54: List[Int] = List(1, 2, 3, 6, 7, 8)

scala> ls.sortBy(x => -x)

res55: List[Int] = List(8, 7, 6, 3, 2, 1)

scala> ls

res56: List[Int] = List(6, 2, 1, 3, 8, 7)

scala> val sw = List(("h",2),("r",1),("m",4))

sw: List[(String, Int)] = List((h,2), (r,1), (m,4))

scala> sw.sortBy(x => x._2)

res57: List[(String, Int)] = List((r,1), (h,2), (m,4))

scala> sw.sortWith((x,y) => x._2 > y._2)

res58: List[(String, Int)] = List((m,4), (h,2), (r,1))

scala> val sw = List(("h",2),("r",2),("m",4))

sw: List[(String, Int)] = List((h,2), (r,2), (m,4))

scala> sw.groupd(2)

<console>:19: error: value groupd is not a member of List[(String, Int)]

       sw.groupd(2)

          ^

scala> sw.grouped(2)

res60: Iterator[List[(String, Int)]] = non-empty iterator

scala> sw.grouped(2).toList

res61: List[List[(String, Int)]] = List(List((h,2), (r,2)), List((m,4)))

scala> val l2 = List(1,3,4)

l2: List[Int] = List(1, 3, 4)

scala> l2.fold(0)((x,y) => x+y)

res62: Int = 8

scala> l2.fold(1)((x,y) => x+y)

res63: Int = 9

scala> l2.fold(2)((x,y) => x+y)

res64: Int = 10

scala> ls.fold(2)((x,y) => x-y)

res65: Int = -25

scala> ls

res66: List[Int] = List(6, 2, 1, 3, 8, 7)

scala> l2.fold((x,y) => x-y)

<console>:19: error: missing parameter type

       l2.fold((x,y) => x-y)

                ^

<console>:19: error: missing parameter type

       l2.fold((x,y) => x-y)

                  ^

<console>:19: error: missing argument list for method fold in trait TraversableOnce

Unapplied methods are only converted to functions when a function type is expected.

You can make this conversion explicit by writing `fold _` or `fold(_)(_)` instead of `fold`.

       l2.fold((x,y) => x-y)

              ^

scala> l2.fold(2)((x,y) => x-y)

res68: Int = -6

scala> l2.fold(2)(_+_)

res69: Int = 10

scala> l2.foldLeft(2)(_+_)

res70: Int = 10

scala> l2.foldRight(2)(_+_)

res71: Int = 10

scala> l2

res72: List[Int] = List(1, 3, 4)

scala> l2.fold(0)(_ - _)

res73: Int = -8

scala> l2.foldRight(0)(_ - _)

res74: Int = 2

scala> l2.foldLeft(0)(_ - _)

res75: Int = -8

scala> l2

res76: List[Int] = List(1, 3, 4)

scala> l2.reduce(_+_)

res77: Int = 8

scala> l2.reduce(_-_)

res78: Int = -6

scala> l2

res79: List[Int] = List(1, 3, 4)

scala> l2.aggregate(0)(_+_,_+_)

res80: Int = 8

scala> val l3 = List(6,7,8)

l3: List[Int] = List(6, 7, 8)

scala> l2.zip(l3)

res81: List[(Int, Int)] = List((1,6), (3,7), (4,8))

scala> val l3 = List(6,7,8,9)

l3: List[Int] = List(6, 7, 8, 9)

scala> l2.zip(l3)

res82: List[(Int, Int)] = List((1,6), (3,7), (4,8))

scala> l2

res83: List[Int] = List(1, 3, 4)

scala> l2.sum

res84: Int = 8

其中

scala> l2

res73: List[Int] = List(1, 3, 4)

//相当于 1-(3-(4-0)   右折叠初始值在右

scala> l2.foldRight(0)(_ - _)

res74: Int = 2

//相当于 (0-1)-3)-4)

scala> l2.foldLeft(0)(_ - _)

res75: Int = -8

六、Set

    无序的，不重复的集合

    Set不可变的集合

    val l5 = collection.mutable.HashSet(2,3,4)

    HashSet可变的集合

    remove 删除元素

    -= 删除元素

    ++ 集合相加

    ++= 相加并赋值

例：

scala> val l4 = List(1,2,2,4)

l4: List[Int] = List(1, 2, 2, 4)

scala> val s = Set(2,3,4)

s: scala.collection.immutable.Set[Int] = Set(2, 3, 4)

scala> val s = Set(2,3,3,4)

s: scala.collection.immutable.Set[Int] = Set(2, 3, 4)

scala> s += 5

<console>:19: error: value += is not a member of scala.collection.immutable.Set[Int]

       s += 5

         ^

scala> collection.mutable.Hash

HashEntry   HashMap   HashSet

scala> val l5 = collection.mutable.HashSet(2,3,4)

l5: scala.collection.mutable.HashSet[Int] = Set(2, 3, 4)

scala> l5 += 6

res86: l5.type = Set(2, 6, 3, 4)

scala> l5

res87: scala.collection.mutable.HashSet[Int] = Set(2, 6, 3, 4)

scala> l5,remove(2)

<console>:1: error: ';' expected but ',' found.

l5,remove(2)

  ^

scala> l5.remove(2)

res88: Boolean = true

scala> l5

res89: scala.collection.mutable.HashSet[Int] = Set(6, 3, 4)

scala> l5 -= 3

res90: l5.type = Set(6, 4)

scala> l4

res91: List[Int] = List(1, 2, 2, 4)

scala> l5

res92: scala.collection.mutable.HashSet[Int] = Set(6, 4)

scala> l4 ++ l5

res93: List[Int] = List(1, 2, 2, 4, 6, 4)

scala> l5 ++= Set(2,7)

res94: l5.type = Set(2, 6, 7, 4)

七、Map

    不可变Map:val m = Map[String,Int]("hello"->2,"world"->8)

    可变Map:

    getOrElse：如果有值返回值，没有返回默认值

例：

scala> val m = Map[String,Int]("hello"->2,"Beijing"->8)

m: scala.collection.immutable.Map[String,Int] = Map(hello -> 2, Beijing -> 8)

scala> m("hello")

res95: Int = 2

scala> m("hello") = 4

<console>:19: error: value update is not a member of scala.collection.immutable.Map[String,Int]

       m("hello") = 4

       ^

scala> val m2 = collection.mutable.HashMap[String,Int]()

m2: scala.collection.mutable.HashMap[String,Int] = Map()

scala> m2.put("lisi",18)

res97: Option[Int] = None

scala> m2

res98: scala.collection.mutable.HashMap[String,Int] = Map(lisi -> 18)

scala> m2 += "weight" -> 120

res99: m2.type = Map(lisi -> 18, weight -> 120)

scala> m2.remove("lisi")

res100: Option[Int] = Some(18)

scala> m2

res101: scala.collection.mutable.HashMap[String,Int] = Map(weight -> 120)

scala> m2 -= "weight"

res102: m2.type = Map()

scala> m2

res103: scala.collection.mutable.HashMap[String,Int] = Map()

scala> m2 += "weight" -> 120

res104: m2.type = Map(weight -> 120)

scala> m2.get("weight")

res105: Option[Int] = Some(120)

scala> m2.getOrElse("zhangsan",18)

res106: Int = 18

scala> m2

res107: scala.collection.mutable.HashMap[String,Int] = Map(weight -> 120)

scala> m2 += "zhangsan" -> 28

res108: m2.type = Map(zhangsan -> 28, weight -> 120)

scala> m2.getOrElse("zhangsan",18)

res109: Int = 28

八、元组tuple

    元组中可以是任意元素

    val t = (2,true,"lisi",Unit)

    取元素：t._1

    对偶元组：有两个元素的元组

例：

scala> val t = (2,true,"lisi",Unit)

t: (Int, Boolean, String, Unit.type) = (2,true,lisi,object scala.Unit)

scala> t

res110: (Int, Boolean, String, Unit.type) = (2,true,lisi,object scala.Unit)

scala> t._1

res111: Int = 2

scala> t._3

res112: String = lisi

scala> val t1 = ("lisi",18)

t1: (String, Int) = (lisi,18)

scala> t1.swap

res113: (Int, String) = (18,lisi)

scala> val t3 = Array(("lisi",18),("zhangsan",16))

t3: Array[(String, Int)] = Array((lisi,18), (zhangsan,16))

//求t3中的年龄的和

scala> t3.foldLeft(0)(_+_._2)

res114: Int = 34

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