arrays - Scala 在两个条件下过滤

Question

我想一次在两个条件下过滤我的数据集。

可能吗？

我想要这样的东西：

mystuff = mystuff.filter(_.isX && _.name == "xyz")

Answer 1

使用稍微不那么简洁的 lambda 语法：

mystuff = mystuff.filter(x => (x.isX && x.name == "xyz"))

您可以在此处找到有关 Scala 匿名函数语法的更多详细信息。

Answer 2

虽然根据“myStuff”的不同可能会对性能产生一些影响，但您始终可以过滤两次

mystuff = mystuff.filter(_.isX).filter(_.name == "xyz")

Answer 3

If you need to frequently filter with several predicate, you could define a way of combining them:

case class And[A]( p1: A=>Boolean, p2: A=>Boolean ) extends (A=>Boolean) {
  def apply( a: A ) = p1(a) && p2(a)
}

Here is how to use it to keep only the odd numbers bigger than 10:

scala> (0 until 20) filter And( _ > 10, _ % 2 == 1 )
res3: scala.collection.immutable.IndexedSeq[Int] = Vector(11, 13, 15, 17, 19)

It easy to write Or and Not combinators in the same fashion.