title: String to Date with leading X character
body: <p>I'm trying to convert the <code>Date</code> column to date format but I keep getting an error. I think the problem might be that the date is a character and has an X before the year:</p>
  <pre><code>HMC.Close        Date
  1     39.71 X2007.01.03
  2     40.04 X2007.01.04
  3     38.67 X2007.01.05
  4     38.89 X2007.01.08
  5     38.91 X2007.01.09
  6     37.94 X2007.01.10
  </code></pre>
  <p>This is the code I've been running:</p>
  <pre class="lang-r prettyprint-override"><code>stock_honda &lt;- expand.grid(&quot;HMC&quot; = HMC$HMC.Close) %&gt;%
    &quot;Date&quot; = as.Date(row.names(as.data.frame(HMC))) %&gt;% 
    subset(Date &gt;&quot;2021-02-28&quot; &amp; Date &lt; &quot;2022-03-11&quot;)
  </code></pre>
  <blockquote>
  <p>Error in charToDate(x) :
  character string is not in a standard unambiguous format</p>
  </blockquote>