title: Selecting certain part of a string
body: <p>Given a column of strings in the format: 'a-b-c' where a, b and c can have any number of digits (e.g. 1-22-333, 120009-5555-1), how would I create new two new columns: 'a' and 'b'? </p>
  
  <p>For example, from 1-22-333, I want two outputs: 1 and 22; from 120009-5555-1, I want 120009 and 5555:</p>
  
  <pre><code>String          a      b
  1-22-333        1      22
  120009-5555-1   120009 5555
  </code></pre>