title: Pyspark join two dataframes
body: <p>Assuming I have two dataframes with different levels of information like this:</p>
  <pre><code>df1
    Month       Day    Values
     Jan      Monday     65      
     Feb      Monday     66
     Mar      Tuesday    68
     Jun      Monday     58 
      
  
  df2
    Month       Day     Hour
     Jan      Monday     5    
     Jan      Monday     5       
     Jan      Monday     8
     Feb      Monday     9
     Feb      Monday     9
     Feb      Monday     9
     Mar      Tuesday    10
     Mar      Tuesday    1
     Jun      Tuesday    2                 
     Jun      Monday     7             
     Jun      Monday     8        
  </code></pre>
  <p>I want to join df1 with df2 and transfer the 'Value' information to df2: Each hour of day will get the 'Day' value.</p>
  <p>Expected output:</p>
  <pre><code>   final
        Month       Day     Hour     Value
         Jan      Monday     5         65
         Jan      Monday     5         65
         Jan      Monday     8         65
         Feb      Monday     9         66
         Feb      Monday     9         66
         Feb      Monday     9         66
         Mar      Tuesday    10        68
         Mar      Tuesday    1         68
         Jun      Monday     7         58             
         Jun      Monday     8         58
  </code></pre>