title: add leading zeros to specific rows
body: <p>I have a column that has ids with several numbers followed by a dash and additional numbers. For any id that has three digits before the dash, I want a leading 0. And, for any id that has 1 digit following the -, I want a leading zero added. Below is sample data.</p>
  <pre><code>id
  222-5
  1023-12
  102-22
  1231-9
  </code></pre>
  <p>I want:</p>
  <pre><code>id
  0222-05
  1023-12
  0102-22
  1231-09
  </code></pre>
  <p>I tried using strsplit, but was not successful. Any advice on getting this to work?</p>