在 Scala 的 for 推导式中是否可以使用自增计数器?
比如:
for (element <- elements; val counter = counter+1) yield NewElement(element, counter)
在 Scala 的 for 推导式中是否可以使用自增计数器?
比如:
for (element <- elements; val counter = counter+1) yield NewElement(element, counter)
我相信,你正在寻找在List和其他集合中可用的zipWithIndex
方法。以下是它的使用示例:
scala> val list = List("a", "b", "c")
list: List[java.lang.String] = List(a, b, c)
scala> list.zipWithIndex
res0: List[(java.lang.String, Int)] = List((a,0), (b,1), (c,2))
scala> list.zipWithIndex.map{case (elem, idx) => elem + " with index " + idx}
res1: List[java.lang.String] = List(a with index 0, b with index 1, c with index 2)
scala> for ((elem, idx) <- list.zipWithIndex) yield elem + " with index " + idx
res2: List[java.lang.String] = List(a with index 0, b with index 1, c with index 2)
scala> val elements = List("a", "b", "c", "d")
elements: List[java.lang.String] = List(a, b, c, d)
scala> for (e <- elements; i <- 0 until elements.length) yield (e, i)
res2: List[(java.lang.String, Int)] = List((a,0), (a,1), (a,2), (a,3), (b,0), (b,1), (b,2), (b,3), (c,0), (c,1), (c,2), (c,3), (d,0), (d,1), (d,2), (d,3))