title: ggplot2 geom_smooth line not showing up on my graph
body: <p>I am trying to add a line through my plotted data using <code>geom_smooth</code>, but I am running into difficulty. </p>
  
  <p>Here is my code:</p>
  
  <pre><code>plot.BG = ggplot(data) + geom_point(aes(x=Mass_LT, y=BG, colour=factor(Temp.f)))   
  plot.BG + geom_smooth(method="lm")
  
  BG
  #[1]  79.56304 118.63903  84.03655  95.02984  67.90585  81.39920  74.73497  95.50199
  #[9]  94.51260  88.08051 110.78937  96.89154  73.96888  74.04067  70.19670  69.80033
  #[17]  64.49329  76.58780  98.73740 107.75642  71.05849  98.45971 101.67881 109.35420
  #[25]  79.32484  69.71360  85.94306 101.25704  87.85497 119.07206  85.72013  98.91010
  #[33]  95.27523  84.89955  93.42660 112.82913 121.77451  84.56991  67.66107 102.73335
  
  Mass_LT
  #[1] 0.000 6.154 0.000 2.128 3.169 5.986 1.916 0.000 5.956 0.566 0.000 0.000 0.530 4.813
  #[15] 2.943 2.645 0.605 2.747 0.726 0.000 0.479 0.000 2.195 0.000 0.000 2.636 3.057 2.777
  #[29] 1.909 4.657 0.000 0.000 0.000 0.000 3.203 0.000 0.000 6.157 0.635 0.000
  
  sort(Mass_LT)
  #[1] 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
  #[15] 0.000 0.000 0.479 0.530 0.566 0.605 0.635 0.726 1.909 1.916 2.128 2.195 2.636 2.645
  #[29] 2.747 2.777 2.943 3.057 3.169 3.203 4.657 4.813 5.956 5.986 6.154 6.157
  </code></pre>
  
  <p><code>Temp.f</code> is a factor with 2 levels, The graph and points come out fine, but without a line and can't quite figure out why. Any help would be greatly appreciated.</p>