title: combine two dataframes with same index (unordered)
body: <p>I don't know why this is confusing me so much.  I am trying to combine two dataframes, and both share the same index (although as a note, they may not be in the same order).  </p>
  
  <pre><code>df1 = |firstrow  10|
        |secondrow 15|
  
  df2 = |secondrow  115|
        |firstrow  1000|
  </code></pre>
  
  <p>and I want the resulting dataframe to be:</p>
  
  <pre><code>result = |firstrow  10  1000|
           |secondrow 15   115|
  </code></pre>
  
  <p>I have tried doing this:</p>
  
  <pre><code>df = pd.merge(df1,df2, on="INDEXNAME"), but it throws a KeyError on INDEXNAME
  </code></pre>
  
  <p>thanks!</p>