scala 基础

Posted 2020-09-02 天天好心情

 

// ::链接字符串 链接字符和list

scala> val a = List(1,2,3)
a: List[Int] = List(1, 2, 3)
scala> val b = 0::a
b: List[Int] = List(0, 1, 2, 3)
scala> val c = "x"::"y"::"z" :: Nil
c: List[String] = List(x, y, z)

 

// :::链接两个list Any公共父类

scala> val d = a ::: c
d: List[Any] = List(1, 2, 3, x, y, z)

 

//head 返回第一个元素

scala> d.head
res20: Any = 1

scala> a.head
res21: Int = 1

scala> b.head
res22: Int = 0

 

//tail 除第一个元素以外的其他元素组成的列表-〉伪列表

scala> a.tail
res23: List[Int] = List(2, 3)

scala> b.tail
res24: List[Int] = List(1, 2, 3)

scala> c.tail
res25: List[String] = List(y, z)

 

//isEmpty

scala> a.isEmpty
res26: Boolean = false

scala> Nil.isEmpty
res27: Boolean = true

scala> def checkEmpty(l : List[Int]):String = {
| if(l.isEmpty) ""
| else l.head.toString}
checkEmpty: (l: List[Int])String

scala> checkEmpty(a)
res28: String = 1

 

//filter应用

scala> a
res29: List[Int] = List(1, 2, 3)

scala> a.filter(x=>x%2==1) 
res30: List[Int] = List(1, 3)

 

//toList

scala> "acd1r3wqa".toList
res31: List[Char] = List(a, c, d, 1, r, 3, w, q, a)

 

//isDigit

scala> "acd1r3wqa".toList.filter(x=>Character.isDigit(x))
res33: List[Char] = List(1, 3)

 

//takeWhile

scala> "acd1r3wqa".toList.takeWhile(x=>Character.isDigit(x))
res34: List[Char] = List()

scala> "acd1r3wqa".toList.takeWhile(x=>x != ‘3‘)
res38: List[Char] = List(a, c, d, 1, r)

 

//toUpperCase _通配匿名函数

scala> c
res41: List[String] = List(x, y, z)

scala> c.map(x=>x.toUpperCase)
res42: List[String] = List(X, Y, Z)

scala> c.map(_.toUpperCase)
res43: List[String] = List(X, Y, Z)

 

//list-map/flatMap可以将两层list转为一层/_多层通配

scala> a
res44: List[Int] = List(1, 2, 3)

scala> a.filter(_%2==1).map(_+10)
res45: List[Int] = List(11, 13)

scala> val e =List(a,List(4,5,6))
e: List[List[Int]] = List(List(1, 2, 3), List(4, 5, 6))

scala> e.map(x=>x.filter(_%2==0))
res48: List[List[Int]] = List(List(2), List(4, 6))

scala> e.map(_.filter(_%2==0))
res49: List[List[Int]] = List(List(2), List(4, 6))

scala> e.flatMap(_.filter(_%2==0))
res51: List[Int] = List(2, 4, 6)

 

//Scala reduceLeft与flodLeft

scala> a
res52: List[Int] = List(1, 2, 3)

scala> a.reduceLeft(_+_)
res53: Int = 6

scala> a.reduceLeft((x,y)=>x+y)
res54: Int = 6

 

//flodLeft 类型与最左边参数类型一致

scala> a.foldLeft(0)(_+_)
res55: Int = 6

scala> a.foldLeft(1)(_+_)
res56: Int = 7

scala> a.foldLeft(4)(_+_)
res57: Int = 10

scala> a.foldLeft(4.0)(_+_)
res58: Double = 10.0

 

// Scala Rang与Stream
//Scala Rang

scala> 1 to 10
res59: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> 1 to 10 by 2
res60: scala.collection.immutable.Range = Range(1, 3, 5, 7, 9)

scala> (1 to 10).toList
res61: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> 1 until 10
res62: scala.collection.immutable.Range = Range(1, 2, 3, 4, 5, 6, 7, 8, 9)

 

//Stream

scala> 1#::2#::3#::Stream.empty
res63: scala.collection.immutable.Stream[Int] = Stream(1, ?)

scala> val stream=(1 to 10000000).toStream
stream: scala.collection.immutable.Stream[Int] = Stream(1, ?)

scala> stream.head
res64: Int = 1

scala> stream.tail
res65: scala.collection.immutable.Stream[Int] = Stream(2, ?)

 

//Scala tuple与map
//tuple

scala> (1,2)
res66: (Int, Int) = (1,2)

scala> 1->2
res67: (Int, Int) = (1,2)

scala> (1,"xiaoming","english",99.9)
res69: (Int, String, String, Double) = (1,xiaoming,english,99.9)

scala> val t=(1,"xiaoming","english",99.9)
t: (Int, String, String, Double) = (1,xiaoming,english,99.9)

scala> t._1
res71: Int = 1

scala> t._2
res72: String = xiaoming

 

=====================================================

scala> def sumSq(in:List[Int]):(Int,Int,Int)=in.foldLeft((0,0,0))((t,v)=>(t._1+1,t._2+v,t._3+v*v))
sumSq: (in: List[Int])(Int, Int, Int)

scala> a
res84: List[Int] = List(1, 2, 3)

scala> sumSq(a)
res85: (Int, Int, Int) = (3,6,14)

scala> sumSq(_)
res86: List[Int] => (Int, Int, Int) = <function1>

 

//map

scala> val f = Map(1->"xiaoming",2->"alisa")
f: scala.collection.immutable.Map[Int,String] = Map(1 -> xiaoming, 2 -> alisa)

scala> f(1)
res88: String = xiaoming

scala> f(2)
res89: String = alisa

scala> f.contains(1)
res90: Boolean = true

scala> f.contains(3)
res91: Boolean = false

scala> f.keys
res92: Iterable[Int] = Set(1, 2)

scala> f.values
res93: Iterable[String] = MapLike(xiaoming, alisa)

scala> f+(5->"eric")
res94: scala.collection.immutable.Map[Int,String] = Map(1 -> xiaoming, 2 -> alisa, 5 -> eric)

scala> f - 1
res95: scala.collection.immutable.Map[Int,String] = Map(2 -> alisa)

scala> f ++ List(3->"nan",4->"frank")
res96: scala.collection.immutable.Map[Int,String] = Map(1 -> xiaoming, 2 -> alisa, 3 -> nan, 4 -> frank)

scala> f
res97: scala.collection.immutable.Map[Int,String] = Map(1 -> xiaoming, 2 -> alisa)

scala> f--List(1,2,3)
res98: scala.collection.immutable.Map[Int,String] = Map()

scala> f ++ List(3->"nan",4->"frank")--List(1,4)
res99: scala.collection.immutable.Map[Int,String] = Map(2 -> alisa, 3 -> nan)

 

//快速排序

scala> def qSort(a:List[Int]):List[Int]= if (a.length<2)a else qSort(a.filter(_<a.head))++ a.filter(_==a.head)++ qSort(a.filter(_>a.head))
qSort: (a: List[Int])List[Int]

scala> qSort(List(1,4,35,76,43,21,53,6))
res81: List[Int] = List(1, 4, 6, 21, 35, 43, 53, 76)