@swift-4.2.4
import Foundation let json = """ [{ "id": 0, "mode": "high" },{ "id": 1, "mode": "middle" },{ "id": 2, "mode": "moddle" },{ "id": 3, "mode": "low" }] """ enum Mode: String, Decodable { case high case middle case low } struct Object: Decodable { let id: Int let mode: Mode? enum CodingKeys: CodingKey { case id, mode } init(from decoder: Decoder) throws { let container = try decoder.container(keyedBy: CodingKeys.self) self.id = try container.decode(Int.self, forKey: .id) self.mode = try? container.decode(Mode.self, forKey: .mode) } } let objects = try! JSONDecoder().decode([Object].self, from: json.data(using: .utf8)!).filter { $0.mode != nil } print(objects)