title: How to find the difference between two arrays after calling a method
body: <p>I'm trying to subtract the earliest date from two arrays:</p>
  
  <pre><code>def days_pending
    start = [object.created_at]
    finish = [Time.now.strftime('%Y-%m-%d')]
    if object.app_sign_date
      start.push(object.app_sign_date)
    end
    if object.submitted_date
      start.push(object.submitted_date)
    end
    if object.inforce_date
      finish.push(object.inforce_date)
    end
    if object.closed_date
      finish.push(object.closed_date)
    end
    finish.min - start.min
  </code></pre>
  
  <p>I have no problem calling <code>min</code> on the arrays, but have a problem calling the <code>min</code> method and then subtracting. I get <code>NoMethodError: undefined  method</code>-' for "2015-01-01":String`.</p>