title: Merging / Appending data frames with unequal columns ,
body: <p>DataFrame 1   (Index is a <strong>date</strong>)</p>
  <pre><code>    date        Apple    Oranges ... Col100
      2020-01-01   9        10
      2002-01-02   5        12 
      ...
      2002-12-10   14       10
  </code></pre>
  <p>Dataframe 2</p>
  <pre><code>   date        Apple    Banana   Kiwi     Oranges... Col100
     2002-12-12   16       20       10        15
  </code></pre>
  <p>I want DataFrame 3 as</p>
  <pre><code>    date        Apple    Oranges   Kiwi     Banana ..... Col100 
      2020-01-01   9        10         0         0
      2002-01-02   5        12         0         0
      ...
      2002-12-10   14       10         0         0
      2002-12-12   16       15        10        20
  </code></pre>
  <p>I have tried</p>
  <pre><code>df3 = df1.merge(df2, how = 'outer') 
  </code></pre>
  <p>it just removed my index which I need absolutely.</p>
  <p>Then I tried</p>
  <pre><code>df3 = df1.merge(df2, how = 'outer',right_index=True, left_index=True) 
  </code></pre>
  <p>but this is creating Apple_x, Oranges_y column and not actually appending to existing Apple oranges.
  I can not pass column names while merging since I have 100s of columns in both DFs.</p>