title: Change the shape of legend key for geom_bar in ggplot2
body: <p>I'm trying to change the shape of the legend key from a geom_bar graph. I've looked at multiple answers online but found they didn't work in this case. Let me explain the problem:</p>
  
  <pre><code>df1 = data.frame(person = c("person1", "person2", "person3"),
               variable = "variable1",
               value = c(0.5, 0.3, 0.2))
  
  df2 = data.frame(person = c("person1", "person2", "person3"),
               variable = "variable2",
               value = c(-0.3, -0.1, -0.4))
  </code></pre>
  
  <p>I'm trying to make a stacked barplot where one side is negative. Using ggplot2 I get:</p>
  
  <pre><code>library(ggplot2)
  ggplot() + geom_bar(data = df1, aes(x = person, y = value, fill = variable), stat = "identity") +
    geom_bar(data = df2, aes(x = person, y = value, fill = variable), stat = "identity") +
    scale_fill_manual(values = c("steelblue", "tomato"), breaks = c("variable1","variable2"),
                  labels = c("Variable 1", "Variable 2"))
  </code></pre>
  
  <p>It then looks like this:</p>
  
  <p><a href="https://i.stack.imgur.com/XBoVa.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/XBoVa.png" alt="enter image description here"></a></p>
  
  <p>Now on the right the legend shows squares by default. Is there a way to change this into a circle for instance? </p>
  
  <p>Online I've found the way this usually works is by using</p>
  
  <pre><code>guides(fill = guide_legend(override.aes = list(shape = 1)))
  </code></pre>
  
  <p>Or similar variations. However this doesn't seem to work. If anybody can help that would be great, I've been stuck for quite a while now.</p>