Question

My intention is simple: to get comma seperated values of emaild from list of User objects. I have done this in Java with a for loop and if else conditions.

现在我想在Schala这样做,这样一来就是尝试。

case class User(name: String, email: String)

val userList = List(User("aaa", "[email protected]"),
                    User("bbb", "[email protected]"),
                    User("ccc", "[email protected]"))

现在

val mailIds = userList.foldLeft(""){(a: String, b: User) => ( b.email+","+a) }

发放

[email protected],[email protected],[email protected],

(note the comma at the end.)

以及

val mailids = userList.map(x => x.email).reduceLeft(_+","+_)

发放

[email protected],[email protected],[email protected]

i 仅使用reduceLeft进行审判 ......

val emailids = userList.reduceLeft((emails: String, user: User) => emails+", "+user.email)

但它投下了汇编错误。

type mismatch;  found   : (String, User) => java.lang.String  required: (java.io.Serializable, User) => java.io.Serializable

因此,在上述情况下,是否有使用<代码>reduceLeft的<><><><>>>>>>><>>> >>>>> ><>>> > > 。

Answer 1

No, reduceLeft is a foldLeft where the accumulator is the first element of the collection. In your case this first element is a User and you have to pass an argument of the same type for the next step of the iteration. That is why you get a type missmatch.
You can do the map within a lazy collection and reduce this like the following:

val mailIds = userList.view map (_.email) reduceLeft (_ + "," + _)

http://www.un.org Jessie Eichar写道,在这方面,“指导。

http://www.ohchr.org。

如果不收集 la,将通过以下方式删除最后 com:

val rawMailIds = userList.foldLeft("")((acc, elem) => acc + elem.email + ",")
val mailIds = rawMailIds.substring(0, rawMailIds.length - 1)

Answer 2

为什么不要把地图结合起来,减少? 无论如何,你的问题是,你的<代码>redLeft<>/code”只有版本才能显示其初步价值。

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