Question

我正在尝试读取json文件，以便在scala中计算一些指标。我设法读取了文件并进行了一些外部过滤，但我在理解如何过滤嵌套列表和地图时遇到了麻烦。

这是示例代码（真正的json更长）：

  val rawData = """[
  {
    "technology": "C",
    "users": [
    {
      "rating": 5,
      "completed": false,
      "user": {
        "id": 11111,
        "paid": true
      }
    },
    {
      "rating": 4,
      "completed": false,
      "user": {
        "id": 22222,
        "paid": false
      }
    }
    ],
    "title": "CS50"
  },
  {
    "technology": "C++",
    "users": [
    {
      "rating": 3,
      "completed": true,
      "user": {
        "id": 33333,
        "paid": false
      }
    },
    {
      "rating": 5,
      "completed": true,
      "user": {
        "id": 44444,
        "paid": false
      }
    }
    ],
    "title": "Introduction to C++"
  },
  {
    "technology": "Haskell",
    "users": [
    {
      "rating": 5,
      "completed": false,
      "user": {
        "id": 55555,
        "paid": false
      }
    },
    {
      "rating": null,
      "completed": true,
      "user": {
        "id": 66666,
        "paid": false
      }
    }
    ],
    "title": "Course on Haskell"
  }
  ]"""

  val data = rawData.toString.split("\n").toSeq.map(_.trim).filter(_ != "").mkString("")

我设法得到包含3个标题的列表：

import scala.util.parsing.json._
val parsedData = JSON.parseFull(data)
val listTitles = parsedData.get.asInstanceOf[List[Map[String, Any]]].map( { case e: Map[String, Any] => e("title").toString }  )

这是我的三个问题：

获取这三个书名的列表是一种好方法吗？
如何获取包含每个用户的付费用户数量的列表后3个标题？
如何获取包含以下用户数量的列表完成了后三个标题中的每一个的课程？

预先感谢您的帮助

Answer 1

作为另一个答案的建议，您应该使用play-json库。它功能强大，并具有大量功能，包括对象映射，解析和错误处理。

  import play.api.libs.json._
  import play.api.data.validation.ValidationError

  case class User(id: String, paid: Boolean)
  object User {
    implicit val format: OFormat[User] = Json.format[User]
  }

  case class UserCourseStat(rating: Int, completed: Boolean, user: User)
  object UserCourseStat {
    implicit val format: OFormat[UserCourseStat] = Json.format[UserCourseStat]
  }

  case class Data(technology: String, title: String, users: List[UserCourseStat])
  object Data {
    implicit val format: OFormat[Data] = Json.format[Data]
  }

  val jsString = """[{"technology":"C","users":[{"rating":5,"completed":false,"user":{"id":11111,"paid":true}},{"rating":4,"completed":false,"user":{"id":22222,"paid":false}}],"title":"CS50"},{"technology":"C++","users":[{"rating":3,"completed":true,"user":{"id":33333,"paid":false}},{"rating":5,"completed":true,"user":{"id":44444,"paid":false}}],"title":"Introduction to C++"},{"technology":"Haskell","users":[{"rating":5,"completed":false,"user":{"id":55555,"paid":false}},{"rating":null,"completed":true,"user":{"id":66666,"paid":false}}],"title":"Course on Haskell"}]"""

  val rowData: JsValue = Json.parse(jsString)

  rowData.validate[List[Data]] match {
    case JsSuccess(dataList: List[Data], _) =>
      val chosenTitles = List("Course on Haskell", "Introduction to C++", "CS50")

      //map of each chosen title to sequence of it's users
      val chosenTitleToUsersMap = chosenTitles.map { title =>
        title -> dataList.filter(_.title == title)
          .flatMap(_.users.map(_.user))
          .toSet
      }.toMap
      //map of each chosen title to sequence of it's paid users
      val chosenTitleToPaidUsersMap = chosenTitleToUsersMap.map { case (title, users) =>
        title -> users.filter(_.paid)
      }

      //Calculate users who have completed each of the chosen title
      val allUsers = dataList.flatMap(_.users.map(_.user)).toSet

      val usersWhoCompletedAllChosenTitles = allUsers.filter{ user =>
        chosenTitles.forall { title =>
          chosenTitleToUsersMap.get(title).flatten.contains(user)
        }
      }

    case JsError(errors: Seq[(JsPath, Seq[ValidationError])]) =>
      //handle the error case
      ???
  }

关于您的3个问题：

获取这三个书名的列表是一种好方法吗？

我在那里看到2个不安全的操作，asInstanceOf和e（“ title”），后一个是因为未使用Map的.get（key）方法，如果找不到键，它将抛出异常。 >

如何获取包含后3个标题中每个标题的付费用户数量的列表？

在上面的名为“ chosenTitleToPaidUsersMap”的值中进行了评估

如何获取包含后三个标题中的每一个都已完成课程的用户数的列表？

在上面的名为“ usersWhoCompletedAllChosenTitles”的值中评估

Answer 2

您可以使用play-json库来解析和检索所需的字段。例如：

import play.api.libs.json.Json

val rawData1 = Json.parse("""[{"technology":"C","users":[{"rating":5,"completed":false,"user":{"id":11111,"paid":true}},{"rating":4,"completed":false,"user":{"id":22222,"paid":false}}],"title":"CS50"},{"technology":"C++","users":[{"rating":3,"completed":true,"user":{"id":33333,"paid":false}},{"rating":5,"completed":true,"user":{"id":44444,"paid":false}}],"title":"Introduction to C++"},{"technology":"Haskell","users":[{"rating":5,"completed":false,"user":{"id":55555,"paid":false}},{"rating":null,"completed":true,"user":{"id":66666,"paid":false}}],"title":"Course on Haskell"}]""")

val resultedList = (rawData1 \\ "title").toList.map(_.as[String])

Answer 3

我建议您使用json4s库。它允许您将数据提取到案例类中：

import org.json4s.jackson.JsonMethods.parseOpt
import org.json4s.DefaultFormats
implicit val formats = DefaultFormats

case class Tech(technology: String, users: Seq[TechUser], title: String)
case class TechUser(rating: Option[Int], completed: Boolean, user: UserInfo)
case class UserInfo(id: Int, paid: Boolean)

val rawData = """..."""
val Some(json) = parseOpt(rawData)
val Some(data) = json.extractOpt[List[Tech]]

完成此操作后，data是常规的Scala数据结构，您可以根据需要对其进行操作。例如，如果要查找哪个用户的ID被5整除的用户，则可以这样做：

data.find(_.users.exists(_.user.id % 5 == 0)).map(_.title)
// Result: Some("Course on Haskell")

您对这三个问题的答案就像这样，只是一线而已，但是我作为练习来留给您。

如何在Scala中过滤嵌套的列表和地图

3 个答案: