Scala常用List列表操作方法日常开发场景

创建列表

1. scala> val days = List("Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday")

2. days: List[String] = List(Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday)

创建空列表

1. scala> val l = Nil

2. l: scala.collection.immutable.Nil.type = List()

3.  

4. scala> val l = List()

5. l: List[Nothing] = List()

用字符串创建列表

1. scala> val l = "Hello" :: "Hi" :: "Hah" :: "WOW" :: "WOOW" :: Nil

2. l: List[String] = List(Hello, Hi, Hah, WOW, WOOW)

用“:::”叠加创建新列表

1. scala> val wow = l ::: List("WOOOW", "WOOOOW")

2. wow: List[String] = List(Hello, Hi, Hah, WOW, WOOW, WOOOW, WOOOOW)

通过索引获取列表值

1. scala> l(3)

2. res0: String = WOW

获取值长度为3的元素数目

1. scala> l.count(s => s.length == 3)

2. res1: Int = 2

返回去掉l头两个元素的新列表

1. scala> l.drop(2)

2. res2: List[String] = List(Hah, WOW, WOOW)

3.  

4. scala> l

5. res3: List[String] = List(Hello, Hi, Hah, WOW, WOOW)

返回去掉l后两个元素的新列表

1. scala> l.dropRight(2)

2. res5: List[String] = List(Hello, Hi, Hah)

3.  

4. scala> l

5. res6: List[String] = List(Hello, Hi, Hah, WOW, WOOW)

判断l是否存在某个元素

1. scala> l.exists(s => s == "Hah")

2. res7: Boolean = true

滤出长度为3的元素

1. scala> l.filter(s => s.length == 3)

2. res8: List[String] = List(Hah, WOW)

判断所有元素是否以“H”打头

1. scala> l.forall(s => s.startsWith("H"))

2. res10: Boolean = false

判断所有元素是否以“H”结尾

1. scala> l.forall(s => s.endsWith("W"))

2. res11: Boolean = false

打印每个元素

1. scala> l.foreach(s => print(s + ' '))

2. Hello Hi Hah WOW WOOW

取出第一个元素

1. scala> l.head

2. res17: String = Hello

取出最后一个元素

1. scala> l.last

2. res20: String = WOOW

剔除最后一个元素，生成新列表

1. scala> l.init

2. res18: List[String] = List(Hello, Hi, Hah, WOW)

剔除第一个元素，生成新列表

1. scala> l.tail

2. res49: List[String] = List(Hi, Hah, WOW, WOOW)

判断列表是否为空

1. scala> l.isEmpty

2. res19: Boolean = false

获得列表长度

1. scala> l.length

2. res21: Int = 5

修改每个元素，再反转每个元素形成新列表

1. scala> l.map(s => {val s1 = s + " - 01"; s1.reverse})

2. res29: List[String] = List(10 - olleH, 10 - iH, 10 - haH, 10 - WOW, 10 - WOOW)

生成用逗号隔开的字符串

1. scala> l.mkString(", ")

2. res30: String = Hello, Hi, Hah, WOW, WOOW

反序生成新列表

1. scala> l.reverse

2. res41: List[String] = List(WOOW, WOW, Hah, Hi, Hello)

按字母递增排序

1. scala> l.sortWith(_.compareTo(_) < 0)

2. res48: List[String] = List(Hah, Hello, Hi, WOOW, WOW)