title: How to merge two dataframes with different lengths in python
body: <p>I am trying to merge two weelly DateFrames, which are made-up of one column each, but with different lengths.</p>
  <p>Could I please know how to merge them, maintaining the 'Week' indexing?</p>
  <p>[df1]</p>
  <pre><code>Week              Coeff1      
  1               -0.456662
  1               -0.533774
  1               -0.432871
  1               -0.144993
  1               -0.553376
  ...                   ...
  53              -0.501221
  53              -0.025225
  53               1.529864
  53               0.044380
  53              -0.501221
  [16713 rows x 1 columns]
  </code></pre>
  <p>[df2]</p>
  <pre><code>Week               Coeff    
  1                 0.571707
  1                 0.086152
  1                 0.824832
  1                -0.037042
  1                 1.167451
  ...                    ...
  53               -0.379374
  53                1.076622
  53               -0.547435
  53               -0.638206
  53                0.067848
  [63265 rows x 1 columns]
  </code></pre>
  <p>I've tried this code:</p>
  <pre><code>df3 = pd.merge(df1, df2, how='inner', on='Week')
  df3 = df3.drop_duplicates()
  df3
  </code></pre>
  <p>But it gave me a new df (df3) with 13386431 rows × 2 columns</p>
  <p>Desired outcome: A new df which has 3 columns (week, coeff1, coeff2), as df2 is longer, I expect to have some NaNs in coeff1 to fill the gaps.</p>