title: How to search for multiple strings and replace them with nothing within a list of strings
body: <p>I have a column in a dataframe like this:</p>
  
  <pre><code>npt2$name
  #  [1] "Andreas Groll, M.D."
  #  [2] ""
  #  [3] "Pan-Chyr Yang, PHD"
  #  [4] "Suh-Fang Jeng, Sc.D"
  #  [5] "Mostafa K Mohamed Fontanet Arnaud"
  #  [6] "Thomas Jozefiak, M.D."
  #  [7] "Medical Monitor"
  #  [8] "Qi Zhu, MD"
  #  [9] "Holly Posner"
  # [10] "Peter S Sebel, MB BS, PhD Chantal Kerssens, PhD"
  # [11] "Lance A Mynderse, M.D."
  # [12] "Lawrence Currie, MD"
  </code></pre>
  
  <p>I tried <code>gsub</code> but with no luck.
  After doing <code>toupper(x)</code> I need to replace all instances of 'MD' or 'M.D.' or 'PHD' with nothing.</p>
  
  <p>Is there a nice short trick to do it?</p>
  
  <p>In fact I would be interested to see it done on a single string  and how differently it is done in one command on the whole list.</p>