title: Add geom_ribbon to reshape2 data frame
body: <p>I have a data frame (df) in the format</p>
  
  <pre><code>  Date          Cs.137 In.111 I.123  I.131     X99m.Tc min    max
  1 2013-01-03    8.2    6.49   6.97   10.5      15      8.294  7.87930
  2 2013-01-04    8.1    6.47   6.94   10.5      15      8.293  7.87835
  3 2013-01-07    8.1    6.48   6.96   10.5      15      8.292  7.87740
  4 2013-01-08    8.1    6.43   6.91   10.5      15      8.291  7.87645
  5 2013-01-09    8.1    6.49   6.92   10.5      15      8.291  7.87645
  6 2013-01-10    8.1    6.51   6.95   10.5      15      8.290  7.87550
  </code></pre>
  
  <p>I want to plot the measured activities of various isotopes over several dates as  a scatter plot. To do this I reshape the data</p>
  
  <p><code>plot_Data &lt;- melt(df[,c(1,2:6)], id="Date", value.name="Activity", variable.name="Isotope")</code></p>
  
  <pre><code>  Date        Isotope     Activity
  1 2013-01-03  Cs.137      8.2
  2 2013-01-04  Cs.137      8.1
  3 2013-01-07  Cs.137      8.1
  4 2013-01-08  Cs.137      8.1
  5 2013-01-09  Cs.137      8.1
  6 2013-01-10  Cs.137      8.1
  </code></pre>
  
  <p>I then plot this using <code>melt</code> from <code>reshape2</code></p>
  
  <p><code>p &lt;- ggplot(plot_Data, aes(x=Date, y=Activity, col=Isotope)) + geom_point()+ theme_bw()</code>
  <img src="https://i.stack.imgur.com/3oqKR.png" alt="enter image description here"></p>
  
  <p>However, the I also want to show a geom_ribbon to highlight the allowed range for Cs-137 activities (given by min and max in the original data frame). I can create such a ribbon on its own using</p>
  
  <p><code>m &lt;- ggplot(df) + geom_ribbon(data=df, aes(x=Date,ymin=min, ymax = max), alpha = 0.2, fill='blue')</code></p>
  
  <p>However, this is using the original frame pre_melted data frame.</p>
  
  <p>When I try <code>p + geom_ribbon(data=df, aes(x=Date,ymin=min, ymax = max), alpha = 0.2, fill='blue')</code> I get the error message <code>Error in eval(expr, envir, enclos) : object 'Activity' not found</code></p>
  
  <p>How can I overlay the ribbon on the original image?</p>
  
  <p>Here is the original data_frame from which the remaining data can be reconstructed
  <code>structure(list(Date = structure(c(15708, 15709, 15712, 15713, 
  15714, 15715, 15716, 15719, 15720, 15721, 15722, 15723, 15726, 
  15727, 15729, 15730, 15733, 15734, 15735, 15736, 15740, 15741, 
  15743, 15747, 15748, 15749, 15750, 15751, 15754, 15755, 15756, 
  15757, 15758, 15761, 15762, 15764, 15765, 15768, 15769, 15770, 
  15771, 15772), class = "Date"), Cs.137 = c(8.2, 8.1, 8.1, 8.1, 
  8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 
  8.1, 8.1, 8.1, 8.1, 8.2, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8, 
  8.2, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1, 8.1), 
      In.111 = c(6.49, 6.47, 6.48, 6.43, 6.49, 6.51, 6.5, 6.47, 
      6.48, 6.4, 6.48, 6.48, 6.48, 6.49, 6.49, 6.47, 6.48, 6.48, 
      6.5, 6.47, 6.49, 6.55, 6.46, 6.49, 6.48, 6.48, 6.46, 6.48, 
      6.49, 6.44, 6.49, 6.46, 6.45, 6.46, 6.46, 6.43, 6.49, 6.47, 
      6.45, 6.43, 6.44, 6.44), I.123 = c(6.97, 6.94, 6.96, 6.91, 
      6.92, 6.95, 6.93, 6.92, 6.93, 7, 6.97, 6.96, 6.96, 6.94, 
      6.98, 6.97, 6.95, 6.95, 6.94, 6.96, 6.97, 7.01, 6.92, 7, 
      6.98, 6.97, 6.91, 6.99, 6.95, 6.88, 6.96, 6.91, 6.91, 6.93, 
      6.94, 6.94, 6.97, 6.93, 6.93, 6.93, 6.96, 6.94), I.131 = c(10.5, 
      10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.8, 10.5, 
      10.6, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 
      10.6, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 
      10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.5, 10.4, 10.5, 10.4, 
      10.5), X99m.Tc = c(15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 
      15, 15.1, 15, 15, 15.1, 15, 15, 15, 15, 15.1, 15, 15.1, 15, 
      15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 14.9, 15, 
      15, 15, 15, 15, 15), Exp_Act = c(8.294, 8.293, 8.292, 8.291, 
      8.291, 8.29, 8.29, 8.288, 8.288, 8.287, 8.287, 8.286, 8.285, 
      8.284, 8.283, 8.283, 8.281, 8.28, 8.28, 8.279, 8.277, 8.277, 
      8.276, 8.274, 8.273, 8.273, 8.272, 8.272, 8.27, 8.27, 8.269, 
      8.269, 8.268, 8.266, 8.266, 8.265, 8.264, 8.263, 8.262, 8.262, 
      8.261, 8.261), Exp_Act_0.95 = c(7.8793, 7.87835, 7.8774, 
      7.87645, 7.87645, 7.8755, 7.8755, 7.8736, 7.8736, 7.87265, 
      7.87265, 7.8717, 7.87075, 7.8698, 7.86885, 7.86885, 7.86695, 
      7.866, 7.866, 7.86505, 7.86315, 7.86315, 7.8622, 7.8603, 
      7.85935, 7.85935, 7.8584, 7.8584, 7.8565, 7.8565, 7.85555, 
      7.85555, 7.8546, 7.8527, 7.8527, 7.85175, 7.8508, 7.84985, 
      7.8489, 7.8489, 7.84795, 7.84795), Exp_Act_1.05 = c(8.7087, 
      8.70765, 8.7066, 8.70555, 8.70555, 8.7045, 8.7045, 8.7024, 
      8.7024, 8.70135, 8.70135, 8.7003, 8.69925, 8.6982, 8.69715, 
      8.69715, 8.69505, 8.694, 8.694, 8.69295, 8.69085, 8.69085, 
      8.6898, 8.6877, 8.68665, 8.68665, 8.6856, 8.6856, 8.6835, 
      8.6835, 8.68245, 8.68245, 8.6814, 8.6793, 8.6793, 8.67825, 
      8.6772, 8.67615, 8.6751, 8.6751, 8.67405, 8.67405)), row.names = c(NA, 
  -42L), .Names = c("Date", "Cs.137", "In.111", "I.123", "I.131", 
  "X99m.Tc", "Exp_Act", "Exp_Act_0.95", "Exp_Act_1.05"), class = "data.frame")
  </code></p>
  
  <p>Thanks</p>