title: Error in creating grouped bar chart with ggplot
body: <p>Dear Stackoverflow users,</p>
  
  <p>I would like to create group bar chart using ggplot. Here is the sample data</p>
  
  <pre><code>&gt; data
                              X0h     X3h     X6h     X9h    X12h
  aldehyde_dehydrgenase   -0.7970 -0.7423 -0.5425 -0.6721 -0.6804
  lactate_dehydrogenase    0.6737  0.5131  0.5063  0.4767  0.3628
  aldehyde_reductase Akr1  0.4701  0.5694  0.2096  0.2696  0.2492
  
  data &lt;- read.csv("fig2.csv", header=T, row.names=1)
  mat.melted &lt;- melt(as.matrix(data), value.name = "expression", varnames=c('Enz', 'TimePoint'))
  
  ggplot(mat.melted, aes(x=Enz, y=TimePoint, fill=expression)) +  geom_bar(position=position_dodge(), stat="identity", colour='black')
  </code></pre>
  
  <p>This I got from the above
  <a href="https://i.stack.imgur.com/jVHPr.png" rel="nofollow noreferrer">enter image description here</a></p>
  
  <p>The bars should be like as below (created using barplot function on same data)<br>
  <a href="https://i.stack.imgur.com/HBied.png" rel="nofollow noreferrer">enter image description here</a></p>