title: Extract string between /
body: <p>If I have these strings:</p>
  
  <pre><code>mystrings &lt;- c("X2/D2/F4",
                 "X10/D9/F4",
                 "X3/D22/F4",
                 "X9/D22/F9")
  </code></pre>
  
  <p>How can I extract <code>2,9,22,22</code>.  These characters are between the <code>/</code> and after the first character within the <code>/</code>.</p>
  
  <p>I would like to do this in a vectorized fashion and add the new column with <code>transfrom</code> if possible with which I am familiar.</p>
  
  <p>I think this regex gets me somewhere near all the characters within <code>\</code>:</p>
  
  <pre><code>^.*\\'(.*)'\\.*$
  </code></pre>