title: Replicating rows while merging two dataframes
body: <p>I have two datasets ,i have added screenshots below</p>
  
  <p>Macro.csv (Full column lists in image)
  <a href="https://i.stack.imgur.com/YZd9f.png" rel="nofollow noreferrer">Macro.csv</a></p>
  
  <pre><code>  Year-Month  Year  Month  Monthly Nominal GDP Index (inMillion$)  \
  0   2009 - Jan  2009      1                            14421.752895   
  1   2009 - Feb  2009      2                            14389.200466   
  2   2009 - Mar  2009      3                            14340.701639   
  3   2009 - Apr  2009      4                            14326.815525   
  4   2009 - May  2009      5                            14345.904809   
  5   2009 - Jun  2009      6                            14348.530666   
  6   2009 - Jul  2009      7                            14317.372922   
  7   2009 - Aug  2009      8                            14424.284901   
  8   2009 - Sep  2009      9                            14410.777177   
  9   2009 - Oct  2009     10                            14596.605447   
  10  2009 - Nov  2009     11                            14590.432252   
  11  2009 - Dec  2009     12                            14512.495301   
  12  2010 - Jan  2010      1                            14613.991481   
  13  2010 - Feb  2010      2                            14652.880272   
  14  2010 - Mar  2010      3                            14776.317248   
  15  2010 - Apr  2010      4                            14844.531193   
  16  2010 - May  2010      5                            14875.698436   
  17  2010 - Jun  2010      6                            14945.570371   
  18  2010 - Jul  2010      7                            15019.235263   
  19  2010 - Aug  2010      8                            15036.277627   
  20  2010 - Sep  2010      9                            15117.467110   
  21  2010 - Oct  2010     10                            15219.059036   
  22  2010 - Nov  2010     11                            15185.628947   
  23  2010 - Dec  2010     12                            15285.936017   
  24  2011 - Jan  2011      1                            15149.136163   
  25  2011 - Feb  2011      2                            15161.578331   
  26  2011 - Mar  2011      3                            15404.398506   
  27  2011 - Apr  2011      4                            15488.004864   
  </code></pre>
  
  <p>Train.csv</p>
  
  <p><a href="https://i.stack.imgur.com/D4LAG.png" rel="nofollow noreferrer">Train.csv</a></p>
  
  <pre><code>   Year  Month ProductCategory  Sales(In ThousandDollars)
  0    2009      1   WomenClothing                     1755.0
  1    2009      1     MenClothing                      524.0
  2    2009      1   OtherClothing                      936.0
  3    2009      2   WomenClothing                     1729.0
  4    2009      2     MenClothing                      496.0
  5    2009      2   OtherClothing                      859.0
  6    2009      3   WomenClothing                     2256.0
  7    2009      3     MenClothing                      542.0
  8    2009      3   OtherClothing                      921.0
  9    2009      4   WomenClothing                     2662.0
  10   2009      4     MenClothing                      669.0
  11   2009      4   OtherClothing                      914.0
  12   2009      5   WomenClothing                     2732.0
  13   2009      5     MenClothing                      650.0
  14   2009      5   OtherClothing                      989.0
  15   2009      6   WomenClothing                     2220.0
  16   2009      6     MenClothing                      607.0
  17   2009      6   OtherClothing                      932.0
  18   2009      7   WomenClothing                     2164.0
  19   2009      7     MenClothing                      575.0
  20   2009      7   OtherClothing                      901.0
  21   2009      8   WomenClothing                     2371.0
  22   2009      8     MenClothing                      551.0
  23   2009      8   OtherClothing                      865.0
  24   2009      9   WomenClothing                     2421.0
  25   2009      9     MenClothing                      579.0
  26   2009      9   OtherClothing                      819.0
  27   2009     10   WomenClothing                     2579.0
  28   2009     10     MenClothing                      610.0
  29   2009     10   OtherClothing                      914.0
  ..    ...    ...             ...                        ...
  186  2014      3   WomenClothing                     4268.0
  187  2014      3     MenClothing                      702.0
  </code></pre>
  
  <p>In macro.csv you can see i have single record for each month of a year,where as in train.csv i have 3 records for each month of a year.
  I want to merge Macro.csv to Train.csv with all the column fields so that i have 3 records for every month in a year with all the columns which are in Macro.csv.</p>