Question

def interpolate(l:List[Tuple2[String,String]]) : List[Tuple2[java.util.Date, Long]] = {
   val mapped : List[Tuple2[java.util.Date, Long]] = l.map(item => (format.parse(item._1), item._2.toLong ) )
   val results = ListBuffer[Tuple2[java.util.Date, Long]]()
   val last : Option[Tuple2[java.util.Date, Long]] = None
   mapped.foreach( item => 
      if(!last.isEmpty) {

         val daysItem = item._1.getTime() / 1000 / 60 / 60 / 24
         val daysLast = last.get._1.getTime() / 1000 / 60 / 60 / 24
         if( daysItem - daysLast > 1 ) {
           val slope = (item._2 - last.get._2) / (daysItem - daysLast)
           val days = daysLast until daysItem
           val missingChunk : List[Tuple2[java.util.Date, Long]] = days.map( day => (new Date(day * 24 * 60 * 60 * 1000), slope * day)).toList
           results ++= missingChunk
         }

      }

      //results += item
      last = Some(item)
   )

   results.toList
}

错误：

<console>:45: error: value last is not a member of Any
possible cause: maybe a semicolon is missing before `value last'?
             last = Some(item)
             ^

Answer 1

这里有两个问题：

1）多个陈述需要{...}括号：

这

mapped.foreach((item: (Date, Long)) => item
  XXX // OK
  YYY // NO
)

到

mapped.foreach { (item: (Date, Long)) => item
  XXX // OK
  YYY // OK
}

2）val无法重新分配：

这

val last: Option[Tuple2[java.util.Date, Long]] = None

到

var last: Option[Tuple2[java.util.Date, Long]] = None

重构＃1

我会尽量避免使用var。似乎有了这个条件if (last.isDefined)，我们可能会尝试zip自己的列表：

scala> val l = List(1, 2, 3, 4, 5)
scala> l.zip(l.tail)
List[(Int, Int)] = List((1,2), (2,3), (3,4), (4,5))

重构你的例子：

  import java.util.Date

  def interpolate(l: List[(String, String)]): List[(Date, Long)] = {
    val mapped: List[(Date, Long)] = l.map(item => (format.parse(item._1), item._2.toLong))
    val results = ListBuffer[(Date, Long)]()

    mapped.zip(mapped.tail).foreach { case ((lastDate, lastLong), (itemDate, itemLong)) =>
      val daysItem = itemDate.getTime / 1000 / 60 / 60 / 24
      val daysLast = lastDate.getTime / 1000 / 60 / 60 / 24
      if (daysItem - daysLast > 1) {
        val slope = (itemLong - lastLong) / (daysItem - daysLast)
        val days = daysLast until daysItem
        val missingChunk: List[(Date, Long)] = days.map(day => (new Date(day * 24 * 60 * 60 * 1000), slope * day)).toList
        results ++= missingChunk
      }
    }

    results.toList
  }

重构＃2

ListBuffer是一个可变的集合。在我们的场景中，我们似乎正在尝试flatten missingChunk s。

继续重构：

  def interpolate(l: List[(String, String)]): List[(Date, Long)] = {
    val mapped: List[(Date, Long)] = l.map(item => (format.parse(item._1), item._2.toLong))
    val missingChunks = mapped.zip(mapped.tail).map { case ((lastDate, lastLong), (itemDate, itemLong)) =>
      val daysItem = itemDate.getTime / 1000 / 60 / 60 / 24
      val daysLast = lastDate.getTime / 1000 / 60 / 60 / 24
      if (daysItem - daysLast > 1) {
        val slope = (itemLong - lastLong) / (daysItem - daysLast)
        val days = daysLast until daysItem
        days.map(day => (new Date(day * 24 * 60 * 60 * 1000), slope * day)).toList
      } else List.empty[(Date, Long)]
    }

    missingChunks.flatten
  }

Scala不是Any的成员

1 个答案: