在一个scala列表中查找元素,并且知道哪个谓词已经被满足 [英] Finding elements in a scala list and also know which predicate has been satisfied
问题描述
$ $ $ $ $ $ $ $ $ $ $ $ $ $列表(A,B,AA,BB )
val l2 = List(AA,BB,A,B)
def c1(s:String)= s.startsWith(B)
def c2(s:String)= s.length == 2
println(l1.find(s => c1(s)|| c2(s)))
println(l2.find(s => c1(s)|| c2(s)))
一些(B)
一些(AA)
$ b对于l1的情况,我希望有一些返回值(例如一个字符串),表示c1被满足(c2为l2的情况)。
一个可能的解决方案可能是在测试之前定义一个var,并将其设置在c1和c2函数中,但是我想找到一个更功能样式的解决方案,或许返回一个Tuple,如:发现,条件满意)。
感谢您的帮助
解决方案<
Scala 2.8:
def find2p [T](l:List [T],p1:T => Boolean,p2:T => Boolean)=
l.view.map(el =>(el,p1 ),p2(el)))。find(t => t._2 || t._3)
Scala 2.7:
pre $ def $ find $ p $ ,p2:T =>布尔)=
l.projection.map(el =>(el,p1(el),p2(el)))。 t $ __3)
视图
/ projection
确保映射将按需完成,而不是应用于整个列表。
I have the following problem in scala. I have to find the first element in al list which satisfies a predicate function with two conditions in OR. The problem is that I would like to get the element but also know which of the two conditions has been satisfied. Here is a simple example:
val l1 = List("A", "B", "AA", "BB")
val l2 = List("AA", "BB", "A", "B")
def c1(s: String) = s.startsWith("B")
def c2(s: String) = s.length == 2
println(l1.find(s => c1(s) || c2(s)))
println(l2.find(s => c1(s) || c2(s)))
result is:
Some(B)
Some(AA)
For the l1 case I would like to have some return value (a String for example) indicating that c1 was satisfied (c2 for the l2 case). A possible solution could be to define a var before the test and set it within the c1 and c2 functions, but I would like to find a more "functional style" solution, maybe something that return a Tuple like: (element found, condition satisfied).
Thanks in advance for the help
I'd do this:
Scala 2.8:
def find2p[T](l: List[T], p1: T => Boolean, p2: T => Boolean) =
l.view.map(el => (el, p1(el), p2(el))).find(t => t._2 || t._3)
Scala 2.7:
def find2p[T](l: List[T], p1: T => Boolean, p2: T => Boolean) =
l.projection.map(el => (el, p1(el), p2(el))).find(t => t._2 || t._3)
The view
/projection
ensures that the mapping will be done on-demand, instead of being applied to the whole list.
这篇关于在一个scala列表中查找元素,并且知道哪个谓词已经被满足的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋!