title: Why DataFrame columns must be unique for json convert?
body: <p>After combining two dataframes, I have this dataframe:</p>
  
  <pre><code>ip                 accountname      name      gsm
  192.168.1.1        aaaa             john doe  850
  192.168.1.2        bbbb             jane doe  860
  </code></pre>
  
  <p>I want to convert dataframe to json:</p>
  
  <pre><code>json_df = df3.set_index('ip').T.to_json()
  </code></pre>
  
  <p>And I have : </p>
  
  <pre><code>ValueError: DataFrame columns must be unique for orient='columns'.
  </code></pre>
  
  <p>IPs are unique in dataframe. Index column is unique. How can I avoid this error? any advice would be appreciated.</p>