title: Plotting a simple time series in ggplot.
body: <p>I am trying to plot a simple time series using <code>ggplot()</code> or <code>qplot()</code>. The horizontal axis will be the date and the vertical axis a number, a simple line chart will suffice.
  Normally, one would need to melt the rectangle data before using <code>ggplot()</code>. However, I am stuck with this:</p>
  
  <pre><code>net.t &lt;- structure(c(6, 11, 0, -1, -13), .Names = c("2011-09-01", "2011-12-01", 
  "2012-03-01", "2012-06-01", "2012-09-01"))
  
  net.t.m &lt;- melt(net.t,id="var")
  
  #After melting 'net.t', it became a vector or array? how to plot that?
  
  qplot(net.t.m,main="Net Promotion Score")+geom_smooth(se=F, size=1.5)
  nps.t+labs(y="NPS",x="Year Quarter")+geom_text(aes(label =value),size = 3, vjust = -1)
  </code></pre>