title: Remove strings and special characters from multiple columns
body: <p>I want to remove strings and special characters from multiple columns (which contain <code>nan</code> values). I only want the numbers to be present. Below is one of my columns. Any help will be appreciated!</p>
  <pre><code>    OTHER
      0   $300.00
      1   $850.00
      2   $550.00
      3   nan
      4   $1,250.00
      5   $81.00
  </code></pre>
  <p>Expected outcome:</p>
  <pre><code>    OTHER
      0   300.00
      1   850.00
      2   550.00
      3   
      4   1250.00
      5   81.00
  </code></pre>