Convert RDD to JSON Object - json

Question

I have an RDD of type RDD[(String, List[String])].
Example:
(FRUIT, List(Apple,Banana,Mango))
(VEGETABLE, List(Potato,Tomato))
I want to convert the above output to json object like below.
{
"categories": [
{
"name": "FRUIT",
"nodes": [
{
"name": "Apple",
"isInTopList": false
},
{
"name": "Banana",
"isInTopList": false
},
{
"name": "Mango",
"isInTopList": false
}
]
},
{
"name": "VEGETABLE",
"nodes": [
{
"name": "POTATO",
"isInTopList": false
},
{
"name": "TOMATO",
"isInTopList": false
},
]
}
]
}
Please suggest the best possible way to do it.
NOTE: "isInTopList": false is always constant and has to be there with every item in the jsonobject.

Answer 1

First I used the following code to reproduce the scenario that you mentioned:
val sampleArray = Array(
("FRUIT", List("Apple", "Banana", "Mango")),
("VEGETABLE", List("Potato", "Tomato")))
val sampleRdd = sc.parallelize(sampleArray)
sampleRdd.foreach(println) // Printing the result
Now, I am using json4s Scala library to convert this RDD into the JSON structure that you requested:
import org.json4s.native.JsonMethods._
import org.json4s.JsonDSL.WithDouble._
val json = "categories" -> sampleRdd.collect().toList.map{
case (name, nodes) =>
("name", name) ~
("nodes", nodes.map{
name => ("name", name)
})
}
println(compact(render(json))) // Printing the rendered JSON
The result is:
{"categories":[{"name":"FRUIT","nodes":[{"name":"Apple"},{"name":"Banana"},{"name":"Mango"}]},{"name":"VEGETABLE","nodes":[{"name":"Potato"},{"name":"Tomato"}]}]}

Answer 2

Since you want a single JSON for you entire RDD, I would start by doing Rdd.collect. Be careful that your set fits in memory, as this will move the data back to the driver.
To get the json, just use a library to traverse your objects. I like Json4s due to its simple internal structure and practical, clean operators. Here is a sample from their website that shows how to traverse nested structures (in particular, lists):
object JsonExample extends App {
import org.json4s._
import org.json4s.JsonDSL._
import org.json4s.jackson.JsonMethods._
case class Winner(id: Long, numbers: List[Int])
case class Lotto(id: Long, winningNumbers: List[Int], winners: List[Winner], drawDate: Option[java.util.Date])
val winners = List(Winner(23, List(2, 45, 34, 23, 3, 5)), Winner(54, List(52, 3, 12, 11, 18, 22)))
val lotto = Lotto(5, List(2, 45, 34, 23, 7, 5, 3), winners, None)
val json =
("lotto" ->
("lotto-id" -> lotto.id) ~
("winning-numbers" -> lotto.winningNumbers) ~
("draw-date" -> lotto.drawDate.map(_.toString)) ~
("winners" ->
lotto.winners.map { w =>
(("winner-id" -> w.id) ~
("numbers" -> w.numbers))}))
println(compact(render(json)))
}