title: Pandas' merge returns a column with _x appended to the name
body: <p>I have to dataframes, <em>df1</em> has columns <em>A, B, C, D...</em> and <em>df2</em> has columns <em>A, B, E, F...</em></p>
  
  <p>The keys I want to merge with are in column <em>A</em>. <em>B</em> is also (most likely) the same in both dataframes. Though this is a big data set I am working on cleaning so I do not have a extremely good overview of everything yet.</p>
  
  <p>I do</p>
  
  <pre><code>merge(df1, df2, on='A')
  </code></pre>
  
  <p>And the results contains a column called B_x. Since the data set is big and messy I haven't tried to investigate how B_x differs from <em>B</em> in <em>df1</em> and <em>B</em> in <em>df2</em></p>
  
  <p>So my question is just in general: what does Pandas mean when it has appended the _x to a column name in the merged dataframe?</p>
  
  <p>Thank you</p>