JSON Play2.1 : sample of function searching for nodes by filtering on key value

gistfile1.scala

// searches for nodes by filtering on key value
def filter(jsv: JsValue, filterFn: String => Boolean): Seq[JsValue] = {
  jsv match {
    case JsObject(fields) => fields.toMap.foldLeft(Seq[JsValue]())((o, pair) => pair match {
      case (key, value) if filterFn(key) => o ++ (value +: (filter(value, filterFn)))
      case (_, value) => o ++ (filter(value, filterFn))
    })
    case _ => Seq[JsValue]()
  }
}

scala> Json.obj("key1" -> Json.obj("toto1" -> "chboing"), "toto2" -> Json.arr( 1, 2, 3))
res31: play.api.libs.json.JsObject = {"key1":{"toto1":"chboing"},"toto2":[1,2,3]}

scala> res31
res32: play.api.libs.json.JsObject = {"key1":{"toto1":"chboing"},"toto2":[1,2,3]}

scala> filter(res31, s => if(s.startsWith("toto")) true else false)
res33: Seq[play.api.libs.json.JsValue] = List("chboing", [1,2,3])