集合 | 易学教程

2019-08-28_20-25-43

数组

定长数组

scala> val arr = new Array[String](10)
arr: Array[String] = Array(null, null, null, null, null, null, null, null, null, null)

scala> val arr = new Array[Int](10)
arr: Array[Int] = Array(0, 0, 0, 0, 0, 0, 0, 0, 0, 0)

scala> val arr = Array("a","b")
arr: Array[String] = Array(a, b)

// 指定初始化数组的数据
scala> val arr = Array.fill(5)(3.14)
arr: Array[Double] = Array(3.14, 3.14, 3.14, 3.14, 3.14)

变长数组

scala> import scala.collection.mutable.ArrayBuffer
import scala.collection.mutable.ArrayBuffer

scala> val arrbf = ArrayBuffer[Int]()
arrbf: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer()

符号使用

scala> arrbf += 1
res22: arrbf.type = ArrayBuffer(1)

scala> arrbf ++= Array(2,3,4)
res24: arrbf.type = ArrayBuffer(1, 2, 3, 4)

scala> arrbf += (5,6,7)
res25: arrbf.type = ArrayBuffer(1, 2, 3, 4, 5, 6, 7)

方法使用

// 尾部追加一个元素
scala> arrbf.append(8)
scala> arrbf
res27: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8)

// 指定下标后插入元素
scala> arrbf.insert(1,9)
scala> arrbf
res29: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 9, 2, 3, 4, 5, 6, 7, 8)

scala> arrbf.insert(1,10,11)
scala> arrbf
res31: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 10, 11, 9, 2, 3, 4, 5, 6, 7, 8)

// 删除尾部3个元素
scala> arrbf.trimEnd(3)
scala> arrbf
res33: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 10, 11, 9, 2, 3, 4, 5)

// 移除index 0 后的 2个元素
scala> arrbf.remove(0,2)
scala> arrbf
res35: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(11, 9, 2, 3, 4, 5)

// 修改index 0 的值为 1
scala> arrbf(0) = 1
scala> arrbf
res37: scala.collection.mutable.ArrayBuffer[Int] = ArrayBuffer(1, 9, 2, 3, 4, 5)

多维数组

scala> val arrs = new Array[Array[Int]](5)
arrs: Array[Array[Int]] = Array(null, null, null, null, null)

scala> val arrs = Array.ofDim[Int](2,3)
arrs: Array[Array[Int]] = Array(Array(0, 0, 0), Array(0, 0, 0))

scala> val arrbfs = new ArrayBuffer[ArrayBuffer[Int]]()
arrbfs: scala.collection.mutable.ArrayBuffer[scala.collection.mutable.ArrayBuffer[Int]] = ArrayBuffer()

方法

数组合并

scala> val arr1 = Array(1 to 3:_*)
arr1: Array[Int] = Array(1, 2, 3)

scala> val arr2 = Array(2 to 4:_*)
arr2: Array[Int] = Array(2, 3, 4)

// union 并集 arr1 - arr2
scala> arr1 union arr2
res16: Array[Int] = Array(1, 2, 3, 2, 3, 4)

// diff 差集 arr1 - arr2 
scala> arr1 diff arr2
res17: Array[Int] = Array(1)

// intersect 交集 arr1 ^ arr2
scala> arr1 intersect  arr2
res19: Array[Int] = Array(2, 3)

map

scala> val arr = Array(1 to 10:_*)
arr: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

// map 对每一个元素应用函数
scala> arr.map(_ + 1)
res38: Array[Int] = Array(2, 3, 4, 5, 6, 7, 8, 9, 10, 11)

reduce

// reduce 对数组里面的元素累加求和
scala> arr.reduce((befer,after) => befer + after)
res39: Int = 55

// 从尾向前进行累 - 
scala> Array(1, 2, 3, 4).reduceRight(_ - _)
res14: Int = -2
// 3 - 4 = -1 
// 2 - -1 = 3 
// 1  - 3 = -2

length

// length 数组长度
scala> Array(1, 2, 3, 4).length
res41: Int = 4

updated

// updated 修改指定下标的值
scala> Array(1,2,3).updated(1,1)
res17: Array[Int] = Array(1, 1, 3)

filter

// filter 筛选符合条件的元素
scala> arr.filter( _ % 2 == 0)
res40: Array[Int] = Array(2, 4, 6, 8, 10)

sum

// sum 求和
scala> arr.sum
res42: Int = 55

max min

// max 数组最大值
scala> arr.max
res43: Int = 10

// min 数组最小值
scala> arr.min
res44: Int = 1

distinct

// distinct 数据去重
scala> Array(1, 2, 3, 4, 5, 2, 3, 4, 5, 6, 7, 8).distinct
res23: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8)

reverse

// reverse 反转数组元素
scala> arr.reverse
res0: Array[Int] = Array(10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

count

// count 统计符合条件元素的数量
scala> Array(1, 2, 3, 4).count( _ % 2 == 0)
res26: Int = 2

sort

// sortWith 排序
scala> arr.sortWith( _ < _)
res45: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> arr.sortWith( _ >  _)
res46: Array[Int] = Array(10, 9, 8, 7, 6, 5, 4, 3, 2, 1)

// sortBy 按照元组的第2个元素来排序，升序
scala> Array((1,2),(0,1),(3,4)).sortBy(_._2)
res48: Array[(Int, Int)] = Array((0,1), (1,2), (3,4))

mkString

// mkString 指定元素之间的分隔符，组成一个字符串。
scala> arr.mkString("--")
res50: String = 1--2--3--4--5--6--7--8--9--10

// 指定将数组组成字符串的 前缀，分隔符，后缀
scala> arr.mkString("<","--",">")
res51: String = <1--2--3--4--5--6--7--8--9--10>

toXxx

// toBuffer 使Array 转为 ArrayBuffer
scala> arr.toBuffer
res54: scala.collection.mutable.Buffer[Int] = ArrayBuffer(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

// toArray 使ArrayBuffer 转为 Array
scala> arr.toBuffer.toArray
res55: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

flatten

// flatten 展平数据
scala> Array(Array(1 to 3:_*),Array(4 to 6:_*)).flatten
res9: Array[Int] = Array(1, 2, 3, 4, 5, 6)

flatMap

// flatMap 先对外层应用 map 然后再对外层应用 flatten
scala> Array(Array(1 to 3:_*),Array(4 to 6:_*)).flatMap(_.map(_ * 2))
res11: Array[Int] = Array(2, 4, 6, 8, 10, 12)

group

scala> val arrs = Array("one 1","two 2","three 3","one 2","two 1").map(_.split(" "))
arrs: Array[Array[String]] = Array(Array(one, 1), Array(two, 2), Array(three, 3), Array(one, 2), Array(two, 1))

scala> arrs.groupBy(_(0))
res0: scala.collection.immutable.Map[String,Array[Array[String]]] = Map(one -> Array(Array(one, 1), Array(one, 2)), three -> Array(Array(three, 3)), two -> Arr
ay(Array(two, 2), Array(two, 1)))

partition,splitAt

// partition 将数据分成两部分，(符号条件,不符合条件)
scala> Array(1 to 10:_*).partition(_ % 2 == 0)
res0: (Array[Int], Array[Int]) = (Array(2, 4, 6, 8, 10),Array(1, 3, 5, 7, 9))

// splitAt 将数据分成两部分，(前n个,剩下的)
scala> Array(1 to 10:_*).splitAt(3)
res1: (Array[Int], Array[Int]) = (Array(1, 2, 3),Array(4, 5, 6, 7, 8, 9, 10))

scan

// scan 从首开始给定初始值0,以reduce的方式计算,并将计算过程的结果生成集合返回
scala> Array(1,2,3).scan(0)(_ + _)
res2: Array[Int] = Array(0, 1, 3, 6)

// 从尾开始
scala> Array(1,2,3).scanRight(0)(_ + _)
res3: Array[Int] = Array(6, 5, 3, 0)

take,slice

// take 取前3个数据
scala> Array(1,2,3,4,5,6,7).take(3)
res4: Array[Int] = Array(1, 2, 3)

// 取后3个数据
scala> Array(1,2,3,4,5,6,7).takeRight(3)
res5: Array[Int] = Array(5, 6, 7)

// slice 取下标为[0,4)的数据
scala> Array(1,2,3,4,5,6,7).slice(0,4)
res9: Array[Int] = Array(1, 2, 3, 4)

forall

// forall 判断元素是否都 小于7
scala> Array(1,2,3,4,5,6,7).forall( _ < 7)
res11: Boolean = false

combinations,permutations

// combinations 返回取2个元素进行排列组合所有可能的种类
scala> Array(1,2,3).combinations(2).toList
res13: List[Array[Int]] = List(Array(1, 2), Array(1, 3), Array(2, 3))

// permutations 返回所有元素排列组合的所有种类
scala> Array(1,2,3).permutations.toList
res15: List[Array[Int]] = List(Array(1, 2, 3), Array(1, 3, 2), Array(2, 1, 3), Array(2, 3, 1), Array(3, 1, 2), Array(3, 2, 1))

// 按照指定要求生成数据；
// 第一个参数：每个list的元素个数为3，第二个参数：选取规则与上一个listindex相差2
// 1 2 3 4 5 6 7 8 9 10
// list0   1  2  3
// listt1  3  4  5
scala> List(1 to 10:_*).sliding(3,2).toList
res22: List[List[Int]] = List(List(1, 2, 3), List(3, 4, 5), List(5, 6, 7), List(7, 8, 9), List(9, 10))

// 参数1和参数2相同的情况
scala> List(1 to 10:_*).grouped(3).toList
res24: List[List[Int]] = List(List(1, 2, 3), List(4, 5, 6), List(7, 8, 9), List(10

// 自定义 case class

scala> case class Book(name: String,num: Int)
defined class Book

scala> val book = Array(Book("语文", 12),Book("数学", 13),Book("英语", 15))
book: Array[Book] = Array(Book(语文,12), Book(数学,13), Book(英语,15))

// 取num的最大值
scala> book.maxBy(_.num)
res1: Book = Book(英语,15)

// 取num的最小值
scala> book.minBy(_.num)
res2: Book = Book(语文,12)

// 按照num 升序排序
scala> book.sortBy(_.num)
res3: Array[Book] = Array(Book(语文,12), Book(数学,13), Book(英语,15))

scala> book.sortWith((book1,book2) => book1.num < book2.num)
res6: Array[Book] = Array(Book(语文,12), Book(数学,13), Book(英语,15))

scala集合和java集合相互转换

// 导入scala转java的隐式转换包。
scala> import scala.collection.JavaConverters._
import scala.collection.JavaConverters._

// scala List 对应 java List
scala> val javaList = List(1 to 5:_*).asJava
javaList: java.util.List[Int] = [1, 2, 3, 4, 5]

// java List 对应 scala Buffer
scala> val scalaBuffer = javaList.asScala
scalaBuffer: scala.collection.mutable.Buffer[Int] = Buffer(1, 2, 3, 4, 5)

其他类型转换：https://blog.csdn.net/u013013024/article/details/80452019

List

增

scala> val left = List(1 to 5:_*)
left: List[Int] = List(1, 2, 3, 4, 5)

scala> val right = List(6 to 10:_*)
right: List[Int] = List(6, 7, 8, 9, 10)

// 连接两个list
scala> left ++ right
res0: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> left ::: (right)
res5: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

// 调换方向连接两个list
scala> left.++:(right)
res4: List[Int] = List(6, 7, 8, 9, 10, 1, 2, 3, 4, 5)

scala> left.:::(right)
res9: List[Int] = List(6, 7, 8, 9, 10, 1, 2, 3, 4, 5)

// 尾部添加元素
scala> left :+ 11
res12: List[Int] = List(1, 2, 3, 4, 5, 11)

// 头部添加元素
scala> left.+:(11)
res15: List[Int] = List(11, 1, 2, 3, 4, 5)

scala> left.::(11)
res17: List[Int] = List(11, 1, 2, 3, 4, 5)

删

scala> val list = List(3 to 10:_*)
list: List[Int] = List(3, 4, 5, 6, 7, 8, 9, 10)

scala> val list1 =  List(3,4,5,1,2)
list1: List[Int] = List(3, 4, 5, 1, 2)

// 从首部删除n个数据
scala> list.drop(4)
res18: List[Int] = List(7, 8, 9, 10)

// 从尾部删除n个数据
scala> list.dropRight(3)
res20: List[Int] = List(3, 4, 5, 6, 7)

// 从左往右匹配,直到匹配到不符合条件的数据,保留后面的数据
scala> list.dropWhile(_ < 6)
res25: List[Int] = List(6, 7, 8, 9, 10)

scala> l.dropWhile(_ < 4)
res27: List[Int] = List(4, 5, 1, 2)

修改查询

scala> val list = List(2 to 6:_*)
list: List[Int] = List(2, 3, 4, 5, 6)

// 通过下标获取数据
scala> list(0)
res28: Int = 2

// 默认不可修改
scala> List
res29: scala.collection.immutable.List.type = scala.collection.immutable.List$@2fc2bb2f

scala> list(0) = 0
<console>:13: error: value update is not a member of List[Int]
       list(0) = 0

常用方法

scala> val list = List(3 to 10:_*)
list: List[Int] = List(3, 4, 5, 6, 7, 8, 9, 10)

// 获取前n个数据
scala> list.take(3)
res31: List[Int] = List(3, 4, 5)

// 条件获取
scala> list.takeWhile( _ < 5)
res36: List[Int] = List(3, 4)

scala> list.takeWhile( _ > 5)
res37: List[Int] = List()

// 元素转换为字符
scala> list.mkString
res38: String = 345678910

// 统计符合条件的数据的数量
scala> list.count( _ % 2 == 0)
res39: Int = 4

// 累加计算
scala> list.sum
res42: Int = 52

scala> val lis = "a" :: ("b" :: ("c" :: Nil))
lis: List[String] = List(a, b, c)

scala> val list = List("One Line","Two line","Three line")
list: List[String] = List(One Line, Two line, Three line)

scala> list.map(_.split(" "))
res49: List[Array[String]] = List(Array(One, Line), Array(Two, line), Array(Three, line))

scala> list.flatMap(_.split(" "))
res51: List[String] = List(One, Line, Two, line, Three, line)

scala> list.map(_.toUpperCase)
res50: List[String] = List(ONE LINE, TWO LINE, THREE LINE)

Set集合

Set

元素不可重复
插入的数据无序

```scala
// 添加元素
scala> Set() + 1
res44: scala.collection.immutable.Set[Int] = Set(1)

```

LinkedHashSet

// LinkedHashSet 可记住插入的顺序

scala> var set = scala.collection.mutable.LinkedHashSet() + 1
set: scala.collection.mutable.LinkedHashSet[Int] = Set(1)

scala> set + 2
res46: scala.collection.mutable.LinkedHashSet[Int] = Set(1, 2)

SortedSet

// SortedSet 插入的数据会自动升序排序

scala> scala.collection.immutable.SortedSet(3,4,1,2,5,0)
res48: scala.collection.immutable.SortedSet[Int] = TreeSet(0, 1, 2, 3, 4, 5)

自定义排序

def main(args: Array[String]): Unit = {

    // 默认使用 Person里面compare方法的比较规则
    val set = SortedSet[Person]()

    // 使用重写Ordering的compare的规则
    //    var set = SortedSet[Person]()(new Ordering[Person] {
    //      override def compare(x: Person, y: Person): Int = {
    //        var diff = x.getName.compareTo(y.getName) // 默认按照name升序排序
    //        if (diff == 0) { // name相同时按照 age 升序排序
    //          diff = x.getAge.compareTo(y.getAge)
    //        }
    //        diff
    //      }
    //    })

    set += new Person("a", 19)
    set += new Person("b", 21)
    set += new Person("c", 19)
    set += new Person("e", 19)
    set += new Person("c", 17)
    set += new Person("d", 20)

    set.foreach(println)
}


class Person extends Ordered[Person] {

    private var name: String = _
    private var age: Int = _

    def this(name: String, age: Int) {
        this()
        this.name = name
        this.age = age
    }

    def getName = name

    def getAge = age

    override def toString: String = {
        s"$name,$age"
    }

    override def compare(that: Person): Int = {
        var diff = this.age.compareTo(that.age)
        if (diff == 0) {
            diff = this.name.compareTo(that.name)
        }
        diff
    }
}

Map

不可变Map,其值不能被改变

scala> val map = Map("k1" -> "value1","k2" -> "value2","k3" -> "value3")
map: scala.collection.immutable.Map[String,String] = Map(k1 -> value1, k2 -> value2, k3 -> value3)

scala> val map = Map(("k1" -> "value1"),("k2" -> "value2"),("k3" -> "value3"))
map: scala.collection.immutable.Map[String,String] = Map(k1 -> value1, k2 -> value2, k3 -> value3)

scala> "k" -> "value"
res56: (String, String) = (k,value)

scala> val map = Map(("k1","value1"),("k2","value2"),("k3","value3"))
map: scala.collection.immutable.Map[String,String] = Map(k1 -> value1, k2 -> value2, k3 -> value3)

可变Map

scala> val map = scala.collection.mutable.Map(("k1","value1"),("k2","value2"),("k3","value3"))
map: scala.collection.mutable.Map[String,String] = Map(k2 -> value2, k1 -> value1, k3 -> value3)

scala> val map = scala.collection.mutable.Map[String,Int]()
map: scala.collection.mutable.Map[String,Int] = Map()

scala> val map = scala.collection.mutable.HashMap[String,Int]()
map: scala.collection.mutable.HashMap[String,Int] = Map()

SortedMap

自动按照key排序

scala> val map = scala.collection.immutable.SortedMap(("a","v1"),("c","v3"),("b","v2"))
map: scala.collection.immutable.SortedMap[String,String] = Map(a -> v1, b -> v2, c -> v3)

LinkedHashMap

记住插入的顺序

scala> val map = scala.collection.mutable.LinkedHashMap(("a","v1"),("c","v3"),("b","v2"))
map: scala.collection.mutable.LinkedHashMap[String,String] = Map(a -> v1, c -> v3, b -> v2)

方法

可变Map方法

scala> val map = scala.collection.mutable.Map(("k1","value1"),("k2","value2"),("k3","value3"))
map: scala.collection.mutable.Map[String,String] = Map(k2 -> value2, k1 -> value1, k3 -> value3)

// 通过key获取值
scala> map.get("k1")
res57: Option[String] = Some(value1)

scala> map.get("k0")
res58: Option[String] = None

// 没有key返回后面的值
scala> map.getOrElse("k0","there is no key!")
res59: String = there is no key!

// 修改值
scala> scala> map("k1") = "v1"
scala> map
res61: scala.collection.mutable.Map[String,String] = Map(k2 -> value2, k1 -> v1, k3 -> value3)

// 添加 k-v
scala> map += ("k4"-> "value4","k5" -> "value5")
res2: map.type = Map(k2 -> value2, k5 -> value5, k4 -> value4, k1 -> v1, k3 -> value3)

// 删除 k-v
scala> map -= "k1"
res3: map.type = Map(k2 -> value2, k5 -> value5, k4 -> value4, k3 -> value3)

不可变Map方法

scala> val map = Map(("k1","value1"),("k2","value2"),("k3","value3"))
map: scala.collection.immutable.Map[String,String] = Map(k1 -> value1, k2 -> value2, k3 -> value3)

// 合并不可变map创建新map
scala> map + ("k4"-> "value4","k5" -> "value5")
res5: scala.collection.immutable.Map[String,String] = Map(k2 -> value2, k5 -> value5, k1 -> value1, k4 -> value4, k3 -> value3)

// 取删除之外的数据，创建新map
scala> map - "k1"
res6: scala.collection.immutable.Map[String,String] = Map(k2 -> value2, k3 -> value3)

// 遍历map的方式
scala> for((k,v) <- map) println(s"k=$k, v=$v")
k=k1, v=value1
k=k2, v=value2
k=k3, v=value3

scala> for((k,_) <- map) println(s"k=$k")
k=k1
k=k2
k=k3

scala> for(k <- map.keySet) println(s"k=$k")
k=k1
k=k2
k=k3

scala> for(v <- map.values) println(s"v=$v")
v=value1
v=value2
v=value3

// 反转map的 key value
scala> for((k,v) <- map) yield (v,k)
res13: scala.collection.immutable.Map[String,String] = Map(value1 -> k1, value2 -> k2, value3 -> k3)

元组

// 创建tuple
scala> val tuple = (1,3.14,"tuple")
tuple: (Int, Double, String) = (1,3.14,tuple)

scala> val tuple = new Tuple3[Int,Double,String](1,3.14,"tuple")
tuple: (Int, Double, String) = (1,3.14,tuple)

// 获取第2个元素，从1开始数
scala> tuple._2
res14: Double = 3.14

// 分别赋值
scala> val (num,doub,str) = (1,3.14,"tuple")
num: Int = 1
doub: Double = 3.14
str: String = tuple

scala> print(num,doub,str)
(1,3.14,tuple)

// 分离出大写和小写字母
scala> "One Two".partition(_.isUpper)
res16: (String, String) = (OT,ne wo)

// 将tuple转换为迭代器遍历
scala> tuple.productIterator.foreach(println)
1
3.14
tuple

来源：https://www.cnblogs.com/studyNotesSL/p/11432903.html

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