为什么我的 Scala 列表在以下代码中消失了? [英] Why does my Scala list disappear in the following code?
本文介绍了为什么我的 Scala 列表在以下代码中消失了?的处理方法,对大家解决问题具有一定的参考价值,需要的朋友们下面随着小编来一起学习吧!
问题描述
val files = new File("data").list()
val filtered = files.filter(name => name.contains("txn"))
val masterList = new ListBuffer[String]
for (file <- filtered) {
val lines = Source.fromFile(new File("data\\" + file), "UTF-16").getLines
val cleaned = lines.filter(!masterList.contains(_))
println("*" + cleaned.length)
cleaned.foreach(println(_))
println("**" + cleaned.length)
cleaned.foreach(masterList.append(_))
}
代码输出如下
*175
**0
我不明白为什么我的列表消失了
I don't understand why my list disappears
推荐答案
cleaned
是一个迭代器.
scala> val cleaned = lines.filter(_!="")
cleaned: Iterator[String] = non-empty iterator
在赋值之后它是非空的.scala 中的迭代器是一次性的——一旦你遍历它(例如通过应用 length
方法)它就变成空的:
Right after assigning it is non-empty. Iterators in scala are single-used - once you traversed it (e.g. by applying length
method) it becomes empty:
scala> cleaned.length
res0: Int = 13
scala> cleaned.length
res1: Int = 0
您可以通过转换为 List 或 Seq(懒惰)来修复该行为:
You can fix that behavior by converting to List, or to Seq (lazy):
scala> val lines=Source.fromFile("bla.txt").getLines
lines: Iterator[String] = non-empty iterator
scala> val cleaned = lines.filter(_!="").toSeq
cleaned: Seq[String] = Stream(first, ?)
scala> cleaned.length
res4: Int = 13
scala> cleaned.length
res5: Int = 13
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