title: need to create a stack bar chart
body: <p>I have three columns with date, var1 and var2. I like to create bar chart date being the x axis and var1 and var2 is y axis. I can do this in line chart but I really like to see how is this done in bar chart with time series data. </p>
  
  <p>My data would be like this:</p>
  
  <pre><code>Date         var1     var2
  2011-12-06  37608.1    12304.2
  2011-12-07  76430.9    28617.7
  2011-12-08  93112.3    33414.6
  2011-12-09 100334.8    28112.0
  2011-12-10  70474.0    23641.4
  2011-12-11 231113.6    78172.5
  </code></pre>
  
  <p>I performed this:</p>
  
  <pre><code>x&lt;-melt(diskIO, id=c("Date"))
  </code></pre>
  
  <p>then</p>
  
  <pre><code>qplot(x = factor(Date), y = value, data = x, geom = "bar", fill = variable)
  </code></pre>
  
  <p>but the date on axis is not really readable, can somebody suggest to organize the date little better.</p>