我是HS的高级成员,也是函数式编程和
Scala的新手.我在
Scala REPL中尝试了一些构造,并需要一些返回响应的指导
//Defined a tuple scala> val x =(2.0,3.0,1) x: (Double,Double,Int) = (2.0,1) //This made sense to me. Result is a list of values that are of type Ints scala> x.productIterator.dropWhile(_.isInstanceOf[Double]).toList res1: List[Any] = List(1) **//This DID NOT make sense to me. Why are Double values included?** scala> x.productIterator.dropWhile(_.isInstanceOf[Int]).toList res0: List[Any] = List(2.0,1) //filter operator seems to work scala> x.productIterator.toList.filter(x => x.isInstanceOf[Double]) res7: List[Any] = List(2.0,3.0)
解决方法
只要它与提供的谓词匹配,
Iterator.dropWhile就会删除任何值,并返回迭代器的其余部分：
Skips longest sequence of elements of this iterator which satisfy
given predicate p,and returns an iterator of the remaining elements.
您传递的提供的谓词对于第一个元素(Double类型)失败,因此它是您实现为List [A]的整个迭代器.
例如,如果您选择在isInstanceOf [Double]时删除,则会收到包含单个元素1的列表：
scala> x.productIterator.dropWhile(_.isInstanceOf[Double]).toList res13: List[Any] = List(1)
