title: Name multiple plots with lapply(ggplot + ggtitle) with nested list name accordingly
body: <p>My question is similar to this question but the difference is that my nested data frames in the list are named.
  <a href="https://stackoverflow.com/questions/42588761/how-can-i-make-multiple-ggplots-from-a-list-of-dataframes-and-have-them-on-one-p">How can I make multiple ggplots from a list of dataframes and have them on one pdf page?</a></p>
  <p>The code below applied the same title to all my plots (I added <code>ggtitle</code> to the original one).<br />
  All the four graphs were named <code>v1</code>, which is the first column name in each <code>df</code>.
  I expected plots to be named <code>df1</code>,<code>df2</code>,..., or perhaps <code>[[1]]</code>, <code>[[2]]</code>,...</p>
  <pre><code>df1 &lt;- data.frame(v1=c(1:5), v2=c(2:6))
  df2 &lt;- data.frame(v1=c(10:50), v2=c(20:60))
  df3 &lt;- data.frame(v1=c(100:500), v2=c(200:600))
  df4 &lt;- data.frame(v1=c(1000:5000), v2=c(2000:6000))
  df.list &lt;- list(df1, df2, df3, df4)
  
  lapply(df.list, function(d) ggplot(data = d, aes(x=v1, y=v2)) + ggtitle(names(d)) + geom_point() )
  </code></pre>
  <p>How do I change my code? Thank you!</p>