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
