title: plotting stacked points using ggplot
body: <p>I have a data frame and I would like to stack the points that have overlaps exactly on top of each other. </p>
  
  <p>here is my example data: </p>
  
  <pre><code>value &lt;- c(1.080251e-04, 1.708859e-01, 1.232473e-05, 4.519876e-03,2.914256e-01, 5.869711e-03, 2.196347e-01,4.124873e-01, 5.914052e-03, 2.305623e-03, 1.439013e-01, 5.407597e-03, 7.530298e-02, 7.746897e-03)
  names = letters[1:7]
  data &lt;- data.frame(names = rep(names,), group = group, value = value, stringsAsFactors = T)
  group &lt;- c(rep("AA", 7) , rep("BB", 7))
  </code></pre>
  
  <p>I am using the following command: </p>
  
  <pre><code>p &lt;- ggplot(data, aes(x = names, y = "", color = group)) + 
  geom_point(aes(size = -log(value)), position = "stack") 
  plot(p)
  </code></pre>
  
  <p>But the stacked circle outlines out of the grid. I want it close or exactly next to the bottom circle. do you have any idea how I can fix the issue? </p>
  
  <p>Thanks, 
  <a href="https://i.stack.imgur.com/hhjqg.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hhjqg.png" alt="enter image description here"></a></p>