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
来源：https://www.cnblogs.com/areyouready/p/10217512.html