title: Hidden /Conditional fields in forms in rails
body: <p>Is it possible to display a form-field only if a specific condition is met?</p>
  
  <p>I want to make something like:</p>
  
  <pre><code>&lt;%= f.input :pregnancies, :as =&gt; :radio, :label =&gt; "Pregnancies", :collection =&gt; [["no", false], ["yes", true]]%&gt;
  
  if :pregnancies = true    
  
  then show this input
  &lt;%= f.input :preg_nr, :label =&gt; "Number of pregnancies" %&gt;
  </code></pre>
  
  <p>Thanks in advance</p>