title: How to plot two histograms together in R?
body: <p>I am using R and I have two data frames: carrots and cucumbers. Each data frame has a single numeric column that lists the length of all measured carrots (total: 100k carrots) and cucumbers (total: 50k cucumbers).</p>
  <p>I wish to plot two histograms - carrot length and cucumbers lengths - on the same plot. They overlap, so I guess I also need some transparency. I also need to use relative frequencies not absolute numbers since the number of instances in each group is different.</p>
  <p>Something like this would be nice but I don't understand how to create it from my two tables:</p>
  <p><img src="https://i.stack.imgur.com/nn4JT.png" alt="overlapped density" /></p>