title: grep part of dataframe and use as title in plot
body: <p>how do I get the name of a dataframe say </p>
  
  <pre><code>mydf.mtcars&lt;-mtcars
  </code></pre>
  
  <p>and grep everything after the <code>.</code> i.e. <code>mtcars</code> and then use this as the title in a plot?</p>
  
  <p>It would be the equivalent of doing</p>
  
  <pre><code>plot(mydf.mtcars,main="mydf")
  </code></pre>
  
  <p>Thanks</p>