title: Add brackets to string in data frame
body: <p>I've got this data frame called df:</p>
  
  <pre><code>ColumnA   ColumnB
  String1   A
  String2   A
  String3   B
  String4   A
  ...       ...
  </code></pre>
  
  <p>Every string in ColumnA have different lenght. I want to put values from ColumnA in brackets if value in ColumnB == A in the same row. If the value in ColumnB == B I want to add square brackets instead. So it will looks like:</p>
  
  <pre><code>ColumnA     ColumnB
  (String1)   A
  (String2)   A
  [String3]   B
  (String4)   A
  ...         ...
  </code></pre>
  
  <p>What's the best way to achive that?</p>