How to iterate org.json4s.JsonAST.JValue which is an array of JSON objects to separately work on each object in Scala?

Question

I have a sample array:

[{
    "abc":"1",
    "de":"1"
},
{
    "fgh":"2",
    "ij":"4"
}]

which is a org.json4s.JsonAST.JValue.

How is it possible to iterate over each object inside the array, to operate on each object separately?

Boxthorn

Answer 1

The following is your json.

scala> json
res2: org.json4s.JValue = JArray(List(JObject(List((abc,JString(1)), (de,JString(1)))),
        JObject(List((fgh,JString(2)), (ij,JString(4))))))

There are several ways.

1. use for syntax

   for {
     JArray(objList) <- json
     JObject(obj) <- objList
   } {
     // do something
     val kvList = for ((key, JString(value)) <- obj) yield (key, value)
     println("obj : " + kvList.mkString(","))
   }
   

2. convert to scala.collection object

   val list = json.values.asInstanceOf[List[Map[String, String]]]
   //=> list: List[Map[String,String]] = List(Map(abc -> 1, de -> 1), Map(fgh -> 2, ij -> 4))
   

   or

   implicit val formats = DefaultFormats
   val list = json.extract[List[Map[String,String]]]
   //=> list: List[Map[String,String]] = List(Map(abc -> 1, de -> 1), Map(fgh -> 2, ij -> 4))
   

   and do something.

   for (obj <- list) println("obj : " + obj.toList.mkString(","))
   

Both outputs are

obj : (abc,1),(de,1)
obj : (fgh,2),(ij,4)

The document of json4s is here.

Menides

Could you help to explain how this pattern matching works? t.filter( a => { a match { case JArray(b) => println(b) ; case other => println(other) } ; true }) . It returns 7 matches. List(JObject(List((abc,JString(1)), (de,JString(1)))), JObject(List((fgh,JString(2)), (ij,JString(4))))) JObject(List((abc,JString(1)), (de,JString(1)))) JString(1) JString(1) JObject(List((fgh,JString(2)), (ij,JString(4)))) JString(2) JString(4) – Cinchonine

Answer 2

You should be able to either cast to JArray

val myArray = myVal.asInstanceOf[JArray]
myArray.arr // the array

or preferably use a scala match so you can confirm the type is correct.

Caecilian

I was about to get into a scala match nightmare to solve this. Like this, it's just perfect. – Doersten