title: Merge pandas dataframe with overwrite of columns
body: <p>What is the quickest way to merge to python data frames in this manner?
  I have two data frames with similar structures (both have a primary key id and some value columns).
  What I want to do is merge the two data frames based on id. Are there any ways do this based on pandas operations? How I've implemented it right now is as coded below:</p>
  
  <pre><code>import pandas as pd
  
  a = pd.DataFrame({'id': [1,2,3], 'letter': ['a', 'b', 'c']})
  b = pd.DataFrame({'id': [1,3,4], 'letter': ['A', 'C', 'D']})
  a_dict =  {e[id]: e for e in a.to_dict('record')}
  b_dict =  {e[id]: e for e in b.to_dict('record')}
  c_dict = a_dict.copy()
  c_dict.update(b_dict)
  c = pd.DataFrame(list(c.values())
  </code></pre>
  
  <p>Here, c would be equivalent to </p>
  
  <pre><code>pd.DataFrame({'id': [1,2,3,4], 'letter':['A','b', 'C', 'D']})
  
     id letter
  0   1      A
  1   2      b
  2   3      C
  3   4      D
  </code></pre>