title: Scala, convert list of dataframe into single dataframe then merge it with another dataframe with a specific column
body: <p>I have a list of dataframe's I want to convert into single dataframe thereafter merge with another dataframe with a specific column of that dataframe and data type should be as it is of new dataframe.Where dfList is List[sql.Dataframe].Any help will be appreciated.  </p>
  
  <pre><code>dfList[sql.Dataframe]=List([A: int]:Dataframe, [B: string]:Dataframe, [C: long]:Dataframe, [D: string]:Dataframe)
  
  dfList = List( +-------+----------+--------+--------+
                 |  A    |     B    |     C  |   D    |
                 +-------+----------+--------+--------+
                 |     41|    912AEQ| 2016022|      UJ|
                 |     82|    912ARD| 2016022|      GH|
                 |    903|    912AYQ| 2016022|      KL|
                 |    454|    912AKK| 2016022|      KL|
                 |     95|    912AHG| 2016022|      KH|
                 +-------+----------+--------+--------+ )
  
  the data type of df is Id: int, v1: string, v2: long, v3: string
  
  df[Dataframe] =            
  +---+---+-----------+-----+
  | Id| v1|    v2     | v3  |
  +---+---+-----------+-----+
  | 11| AS| 0989765498|SDAWQ|
  | 12| GH| 7654998599|TRUDR|
  | 13| IO|10654998580|ABUCK|
  | 14|1JG|65499855101|KLBCK|
  | 15| RT|10265499852|BCKKL|
  +---+---+-----------+-----+            
  
  The newDF will be combination of dfList and df.
  The datatype of newDF should be Id: int, A: int, B: string, C: long, D: string 
  
  
  newDF =
      +---+------+----------+--------+--------+
      | Id| A    |     B    |     C  |   D    |
      +---+------+----------+--------+--------+
      | 11|    41|    912AEQ| 2016022|      UJ|
      | 12|    82|    912ARD| 2016022|      GH|
      | 13|   903|    912AYQ| 2016022|      KL|
      | 14|   454|    912AKK| 2016022|      KL|
      | 15|    95|    912AHG| 2016022|      KH|
      +---+------+----------+--------+--------+
  </code></pre>