title: How to display 0 value in a bar chart using ggplot2
body: <p>I have this data frame called data:</p>
  
  <blockquote>
    <p>head(data)</p>
  </blockquote>
  
  <pre><code>     date         total_sold purchasability visibility
  81 2014-05-01          3              3          3
  82 2014-05-02          2              2          3
  83 2014-05-03          1              2          3
  84 2014-05-04          1              3          3
  85 2014-05-05          3              2          3
  86 2014-05-06          0              0          3
  </code></pre>
  
  <p>And I would like to do a bar chart with x = date and y = total_sold with a color depending on the purchasability. I this ggplot2 to do that :</p>
  
  <pre><code>bar &lt;- ggplot(data = data, aes(x = date, fill=as.factor(purchasability),y = total_sold)) + geom_bar(stat = 'identity')
  </code></pre>
  
  <p>The output is very nice but the problem is that where total_sold = 0 there is not chart and thus no way to know the purchasability. Is it possible to still display a bar (maybe from 0.5 to -0.5) when total_sold = 0 ?</p>
  
  <p>Thanks</p>