title: Spark: Merge 2 dataframes by adding row index/number on both dataframes
body: <p>Q: Is there is any way to merge two dataframes or copy a column of a dataframe to another in PySpark?</p>
  
  <p>For example, I have two Dataframes:</p>
  
  <pre><code>DF1              
  C1                    C2                                                        
  23397414             20875.7353   
  5213970              20497.5582   
  41323308             20935.7956   
  123276113            18884.0477   
  76456078             18389.9269 
  </code></pre>
  
  <p>the seconde dataframe</p>
  
  <pre><code>DF2
  C3                       C4
  2008-02-04               262.00                 
  2008-02-05               257.25                 
  2008-02-06               262.75                 
  2008-02-07               237.00                 
  2008-02-08               231.00 
  </code></pre>
  
  <p>Then i want to add C3 of DF2 to DF1 like this:</p>
  
  <pre><code>New DF              
      C1                    C2          C3                                              
      23397414             20875.7353   2008-02-04
      5213970              20497.5582   2008-02-05
      41323308             20935.7956   2008-02-06
      123276113            18884.0477   2008-02-07
      76456078             18389.9269   2008-02-08
  </code></pre>
  
  <p>I hope this example was clear.</p>