title: Extract last substring between square brackets
body: <p>I've a column of data from which I need to extract a alphnumeric string/factor example </p>
  
  <pre><code>Column x
  [ghjg6] [fdg5] [113gi4lki] great work 
  [xzswedc: acf] [xzt8] [111eerrh5] 
  [asd2] [1] [113vu17hg 115er5lgr 112cgnmbh ] get out
  </code></pre>
  
  <p>I want to get the data in the square brackets <code>[113gi4lki]</code>, <code>[111eerrh5]</code> and <code>[113vu17hg 115er5lgr 112cgnmbh]</code> in a separate column. Please advise.</p>