title: Binary operator '<' cannot be. applied to two 'Any?' operands
body: <p>I try to request data from web, then get an array for four times(they are different), and I tried to put these four arrays in a big array.
  The problem is the four small arrays is not in the right place in the large array. What I thought is to use this function <strong>largeArray.sort</strong> to make the four little ones in the right position.
  Here is my code:</p>
  
  <pre><code>for i in 0..&lt;4{
      Alamofire.request(homeUrl[i], method: .get, parameters: nil, encoding: JSONEncoding.default).responseJSON { (valueGot) in
          switch valueGot.result.isSuccess{
          case true:
              let dataDict = valueGot.result.value as! NSDictionary
              let interestDict = dataDict["interest"] as! NSDictionary
              let issuesArray = interestDict["issues"] as! NSArray
              let todayDict = issuesArray[0] as! NSDictionary
              let articlesArray = todayDict["articles"] as! NSArray
              self.nsmArray.removeAllObjects()
              for oneDict in articlesArray{
                  let model:ArticleModel = Mapper&lt;ArticleModel&gt;().map(JSON: oneDict as! [String:Any])!
                  if model.cover != nil{
                      self.nsmArray.add(model)
                  }
              }
              self.nsmArray.add(i)
                  self.collectionNSMArray.add(self.nsmArray.mutableCopy()                  
              self.allCollectionView?.reloadData()
  
          case false:
              print(valueGot.error ?? "404")
          }
      }
  }       //for循环结束
  </code></pre>
  
  <p>Here's the error:</p>
  
  <pre><code>collectionNSMArray.sort { (s1:NSMutableArray, s2:NSMutableArray) -&gt; Bool in
      return s1.lastObject &lt; s2.lastObject
  }
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/QIvf2.png" alt="enter image description here"></p>
  
  <p>Here's the model I did:</p>
  
  <pre><code>class ArticleModel: Mappable {
  
      var title:String?
      var snippet:String?
      var cover:String?
      var tags:[TagsType]?
      var webUrl:String?
      var appName:String?
      var appIcon:String?
  
  
      required init?(map: Map) {
          mapping(map: map)
      }
      func mapping(map: Map) {
          title &lt;- map["title"]
          snippet &lt;- map["snippet"]
          cover &lt;- map["cover"]
          tags &lt;- map["tags"]
          webUrl &lt;- map["webUrl"]
          appName &lt;- map["appName"]
          appIcon &lt;- map["appIcon"]
      }
  }
  
  class TagsType: Mappable {
  
      var name:String?
  
      required init?(map: Map) {
          mapping(map: map)
      }
      func mapping(map: Map) {
          name &lt;- map["name"]
      }
  }
  </code></pre>