title: How to draw a nice arrow in ggplot2
body: <p>I am creating a <code>ggplot</code> chart where I want to have some arrows between two points. The main task is easily done with <code>geom_line(arrow = arrow())</code>. However, I want to have some "beautiful" thick arrows. Resizing the arrow via <code>size=</code> doesn't help since it messes up the head of the arrow completely. I illustrate my Problems:</p>
  
  <p>Create some sample data and a plot:</p>
  
  <pre><code> NAME &lt;- c("A", "A", "B", "B", "C", "C")
   YEAR &lt;- c(2016, 2011, 2016, 2011, 2016, 2011)
   YEAR &lt;- as.factor(YEAR)
   VALUE &lt;- c(1, 4, 1, 5, 2, 8)
   DATA &lt;- data.frame(NAME, YEAR, VALUE)
  
  ggplot(DATA, aes(x=VALUE, y=NAME)) + 
    geom_point(size=5, aes(colour=YEAR)) +
    geom_line(arrow = arrow(length=unit(0.30,"cm"), ends="first", type = "closed"))
  </code></pre>
  
  <p>The resulting plot looks like that:</p>
  
  <p><img src="https://i.stack.imgur.com/amnYr.png" alt="plot1"></p>
  
  <p>Now I've tried to "thicken" the arrows...</p>
  
  <pre><code>ggplot(DATA, aes(x=VALUE, y=NAME)) + 
    geom_point(size=5, aes(colour=YEAR)) +
    geom_line(arrow = arrow(length=unit(0.30,"cm"), ends="first", type = "closed"), size = 3)
  </code></pre>
  
  <p>That's the result shown here:</p>
  
  <p><img src="https://i.stack.imgur.com/tdxH6.png" alt="plot2"></p>
  
  <p>My question: Is there any way to plot some "beautiful" thick arrows?</p>