title: How to read data with different separators?
body: <p>I have a file looks like:</p>
  
  <pre><code>a 1,2,3,5
  b 4,5,6,7
  c 5,6,7,8
  ...
  </code></pre>
  
  <p>That the separator between 1st and 2nd is '\t', other separators are comma. How can I read this kind of data set as as dataframe having 5 fields.</p>