title: Plotting horizontal graphs with positive and negative values on barplot()
body: <p>I have this data frame with 30 columns, which the first has positive values, the next negative ones and so on. I want to make a horizontal bar plot comparing each of these column in pairs (one positive with one negative).</p>
  
  <p>Reproducible data:</p>
  
  <pre><code>x = 0:600
  y = 0:-600
  
  col1&lt;- sample(x, 40)
  col1
  col2&lt;- sample(y, 40)
  col2
  
  df = as.data.frame(rep(data.frame(col1, col2), 15))
  df
  
  final.data&lt;-colMeans(df, na.rm=T)
  final.data
  </code></pre>
  
  <p>When I try this command:</p>
  
  <pre><code>barplot(final.data, 
      horiz=TRUE, 
      xlim=c(-500,500), 
      xlab="average time (seconds)", 
      axisnames=FALSE)
  </code></pre>
  
  <p>I get something similar to: </p>
  
  <p><a href="https://i.stack.imgur.com/PDUSN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/PDUSN.png" alt="enter image description here"></a></p>
  
  <p>My main question is:</p>
  
  <ol>
  <li>How to make the horizontal bars that I want to compare to be next to each other and not slightly down?</li>
  </ol>
  
  <p>Another related question that I couldn't find the answer to:</p>
  
  <ol start="2">
  <li>How do I add a * in front of the treatments that I saw significant difference?</li>
  </ol>