Scala解惑

1. map中获取index

val x = list.zipWithIndex.flatMap(x => 
  anotherFunction(x._1.param1.param2List.size * x._1.multiplier, 
  x._1, x._1.param1.param2List(x._2)))

2. List转Map， List[Tuple3] to Map[String,String]

val prices = dao.getPricing.map { p => ( p._1.toString, p._2+" $"+p._3)} toMap

val prices: Map[String, String] = dao.getPricing.map {  
   case (id, label, fee) => 
    (id.toString -> (label + " $" + fee))
 } (collection.breakOut)

3. Json序列化

import scala.util.parsing.json.JSONObject
// import scala.util.parsing.json.JSONArray 序列化List类型的对象

val mymap = array.map { 
  case 1 => ("A", 1) 
  case 2 => ("B", 2) 
  case 3 => ("C", 3)
} .toMap
# 只需一行
JSONObject(mymap).toString()

4. Json反序列化

import scala.util.parsing.json.JSON

val json = JSON.parseFull(string) //将JSON格式字符串解读成Some
val any = json.get  //将some格式中的内容get出来，得到一个any类型的值
any match {  
  case map: Map[String, String] =>map //匹配成功返回我们需要的Map类型数据
  case _ => { //匹配失败返回Null值
    println("匹配失败");
    null
  } 
}

5. String.split

split函数主要有两种参数形式：

def split(arg0: String): Array[String]  // 等同于split(arg0, 0)
def split(arg0: String, arg1: Int): Array[String]

• arg0：正则表达式，代表分割的边界
• arg1：限定分割后子串的个数

// 当arg1大于0时，它限制arg0最多成功匹配arg1-1次，也就是说字符串最多被分成arg1个子串。
//此时split会保留分割出的空字符串，直到达到匹配上限
scala> "a-b-c".split("-", 2)
res38: Array[String] = Array(a, b-c)

scala> "a-b-c".split("-", 4)
res39: Array[String] = Array(a, b, c)

scala> "-a-b-c--".split("-", 3)
res40: Array[String] = Array("", a, b-c--)

scala> "-a-b-c--".split("-", 6)
res41: Array[String] = Array("", a, b, c, "", "")

scala> "-a-b-c--".split("-", 5)
res42: Array[String] = Array("", a, b, c, -)

scala> "-a-b-c--".split("-", 8)
res43: Array[String] = Array("", a, b, c, "", "")

// 当arg1等于0时，split函数会尽可能多的匹配arg0，但不再保留处于末尾位置的空字符串
scala> "a-b-c".split("-", 0)
res48: Array[String] = Array(a, b, c)

scala> "a-b-c---".split("-", 0)
res49: Array[String] = Array(a, b, c)

scala> "-a--b--c---".split("-", 0)
res50: Array[String] = Array("", a, "", b, "", c)

scala> "".split("-", 0)
res51: Array[String] = Array("")

// 当arg1小于0时，split函数会尽可能多的匹配arg0，并且保留末尾的空字符串
scala> "a-b-c".split("-", -1)
res52: Array[String] = Array(a, b, c)

scala> "-a--b--c-".split("-", -1)
res53: Array[String] = Array("", a, "", b, "", c, "")

6. Java List to Scala List

Since Scala 2.8 this conversion is now built into the language using:

import scala.collection.JavaConversions._
...
lst.toList.foreach{ node =>   .... }

works. asScala did not work

7. Scala multiMap

// This is your list of (A, B)
val l = List((1, "hi"),
             (2, "there"),
             (1, "what's"),
             (3, "up?"))
// Group it and snip out the duplicate 'A'
// i.e. it initially is Map[A, List[(A, B)]] and we're going to convert it
// to Map[A, Set[B]]
val m = l.groupBy(e => e._1).mapValues(e => e.map(x => x._2).toSet)
println(m)
// Prints: Map(3 -> Set(up?), 1 -> Set(hi, what's), 2 -> Set(there))