在 Scala 中 - 将案例类列表转换为元组列表 [英] In Scala - Converting a case class List into a List of tuples

问题描述

我有一个案例类

case class table(a: String, b: Option[String])

我有一个这种类型的列表 - 让我们称之为 list1

and i have a list of that type - lets call it list1

val list1: List[table] = tabele.get() // just filling the list from an SQL 

现在我想将表"的列表更改为一个简单的 (String,Option[String]) 列表我已经在这个板上找到的是如何将案例类转换为元组像这样:

now I want to change the list of "table" into a simple list of (String,Option[String]) What i allready found on this board was how to convert a case class into a tuple like that:

case class table(a:String, b:Int)
val (str, in) =  table.unapply(table("test", 123)).get()

但我不知道如何在列表上使用它:(我用 foreach 尝试了一些类似的东西:

But i don't know how to use this on a List :( I tried something with foreach like:

val list2: List[(String, Option[String])] = Nil
list1.foreach( x => list2 :: table.unapply(x).get())
'error (String,Option[String]) does not take parameters

所以我的问题是 -> 如何在 List 的每个元组上使用 unapply?

so my question would be -> how can I use unapply on every tuple of a List?

提前致谢

PS:我实际上想更改列表的类型，因为我想在该列表上使用.toMap"- 喜欢:

PS: I actually want to change the type of the list because I want to use ".toMap" on that list - like:

val map1 = list1.toMap.withDefaultValue(None)

错误:

Cannot prove that models.table <:<(T,U)

它适用于 (String, Option[String]) 列表

and it would work for a (String, Option[String]) list

推荐答案

您想转换列表中的每个元素并给出另一个列表.你需要foreach的表亲，map:

You want to convert every element of a list giving another list. You need foreach's cousin, map:

试试:

 list1.map(table.unapply).flatten

这是一种更好的写作方式:

which is a better way of writing:

 list1.map( tbl => table.unapply(tbl) ).flatten

另一种方式是

 list1.map(table.unapply(_).get)

这是什么的简写

 list1.map( tbl => table.unapply(tbl).get )

并且只是使用 for 加入一个版本:(这说明了 unapply 在 for 推导式中的使用方式)

And just to throw in a version using for: (which is illustrative of how unapply is used under the hood in for comprehensions)

 for (table(s,ms) <- list1) yield (s, ms)

这篇关于在 Scala 中 - 将案例类列表转换为元组列表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！