title: creating "radar chart" (a.k.a. star plot; spider plot) using ggplot2 in R
body: <p>I want to create a plot like the one below:</p>
  
  <p><img src="https://i.stack.imgur.com/q34Zx.png" alt="enter image description here"></p>
  
  <p>I know I can use the <a href="http://rgm2.lab.nig.ac.jp/RGM2/func.php?rd_id=fmsb:radarchart" rel="noreferrer"><code>radarchart</code></a> function from <code>fmsb</code> package. I wonder if <code>ggplot2</code> can do so, using polar coordinate? Thanks.</p>