title: ObjectMapper - nested dynamic keys
body: <p>I'm writing in Swift 3.1, using ObjectMapper to map my JSON response to my models.</p>
  
  <p>I'm trying to map this rather complex JSON response with dynamic keys and am hoping to get some feedback on what I'm doing wrong.</p>
  
  <p>A group has statistics about it's progress. It has stats broken down to years and then months. Each month within a year has results, ROI and win. The ROI and win are just percentages but the results key is fixed with the keys below, 1-5, and then some integer as a value.</p>
  
  <p><strong>My JSON</strong></p>
  
  <pre><code>"stats": {
      "2017": {
          "1": {
              "results": {
                  "1": 13,
                  "2": 3,
                  "3": 1,
                  "4": 1,
                  "5": 0
              },
              "roi": 0.40337966202464975,
              "win": 0.8181818181818182
          },
          "2": {
              "results": {
                  "1": 13,
                  "2": 5,
                  "3": 1,
                  "4": 2,
                  "5": 1
              },
              "roi": 0.26852551067922953,
              "win": 0.717948717948718
          }
      }
  }
  </code></pre>
  
  <p><strong>My models</strong></p>
  
  <pre><code>class GroupResponse: Mappable {
      var stats: [String: [String: StatsMonthResponse]]?
  
      func mapping(map: Map) {
          stats   &lt;- map["stats"]
      }
  }
  
  class StatsMonthResponse: Mappable {
      var tips: [String: Int]?
      var roi: Double?
      var win: Double?
  
      func mapping(map: Map) {
          tips    &lt;- map["results"]
          roi     &lt;- map["roi"]
          win     &lt;- map["win"]
      }
  }
  </code></pre>
  
  <p><strong>What I get</strong></p>
  
  <p>The response I get has the stats property in my GroupResponse class, as nil.</p>
  
  <p>What other approach could I do to accomplish this, or change in my implementation to get this done?</p>