Modify Value for a certain key of a Dictionary

playground.swift

//: Playground - noun: a place where people can play

import UIKit
import Foundation

var dictOfProductsForCategory: [Int: [[String:Any]]] = [:]

//I want dictOfProductsForCategory[3183] eventually to be set with 4-items Array
//How can I do this?
var result1: [[String:Any]]? = [["id":5, "title": "Some Title"], ["id":6, "title": "Another Title"]]

var result2: [[String:Any]]? = [["id":7, "title": "Third Title"], ["id":8, "title": "Fourth Title"]]


dictOfProductsForCategory[3183] = result1
print(dictOfProductsForCategory)
dictOfProductsForCategory[3183] += result2 //Error
dictOfProductsForCategory[3183] = dictOfProductsForCategory[3183] +result2 //Error too
// How?