anchor.diff:  
   In MyRecommendation/src/main/scala/***Engine.scala***,
   we define the `ActualResult` which represents the user rating for validation.
  -It stores the list of rating in the validation set for a user.
  +It stores the list of ratings in the validation set for a user.
   
   ```scala
   case class ActualResult(
  
positive.code: 
  ### Implement Data Generate Method in DataSource
  
  In MyRecommendatin/src/main/scala/***DataSource.scala***,
  the method `readEval` method reads, and selects, data from datastore
  and resturns a sequence of (training, validation) data.
  
  ```scala
  case class DataSourceEvalParams(kFold: Int, queryNum: Int)
  
negative.code: data contains rating for all user-item tuples. In contrast, of a system containing
  1000 items, a user may only have rated 20 of them, leaving 980 items unrated. There
  is no way for us to certainly tell if the user likes an unrated product.
  When we examine the evaluation result, it is important for us to keep in mind
  that the final metric is only an approximation of the actual result.
  
  - Recommendation affects user behavior. Suppose you are a e-commerce company and
  