title: plot survival curves with confident interval bars
body: <p>Hi I would have a question.
  I am trying to draw 3 survival curve on the same plot.
  For each plot I would like to add the confident interval.</p>
  
  <p>For this I have a data frame </p>
  
  <pre><code>          dput(df)
      structure(list(lowerA = c(4.1, 4.6, 5.5, 4.7, 5), Group1 = c(4.8, 
  5.4, 6.4, 5.5, 5.7), upperA = c(5.7, 6.3, 7.3, 6.3, 6.6), lowerB = c(6.2, 
  7.1, 8.7, 7.4, 8.2), Group2 = c(7.3, 8.3, 10, 8.6, 9.5), upperB = c(8.6, 
  9.6, 11.4, 9.9, 10.8), lowerC = c(18.3, 19.5, 24.3, 22.9, 25.5
  ), Group3 = c(21.4, 22.5, 27.6, 26.3, 29), upperC = c(24.7, 25.8, 
  31, 29.8, 32.7)), .Names = c("lowerA", "Group1", "upperA", "lowerB", 
  "Group2", "upperB", "lowerC", "Group3", "upperC"), row.names = c("year1", 
  "year2", "year3", "year4", "year5"), class = c("tbl_df", "tbl", 
  "data.frame"))
  </code></pre>
  
  <p>I tried this. It works but it's not beautiful. </p>
  
  <pre><code>ya &lt;- rownames(df)
  xa &lt;- Group1
  z1a &lt;- lowerA
  z2a &lt;- upperA
  
  
  xb &lt;- Group2
  z1b &lt;- lowerB
  z2b &lt;- upperB
  
  
  xc &lt;- Group3
  z1c &lt;- lowerC
  z2c &lt;- upperC
  </code></pre>
  
  #
  
  <pre><code>plot(ya, xa, ylim = c(0,40))
  lines(ya, xa, c)
  # now the confidence bands
  lines(ya, z1a, lty = "dotted")
  lines(ya, z2a, lty = "dotted")
  
  lines(yb, xb, col="green")
  # now the confidence bands
  lines(yb, z1b, lty = "dotted",col="green")
  lines(yb, z2b, lty = "dotted", col="green")
  
  lines(yc, xc, col="red")
  # now the confidence bands
  lines(yc, z1c, lty = "dotted", col="red")
  lines(yc, z2c, lty = "dotted", col="red")
  </code></pre>
  
  <p>Any help? Suggestion?</p>
  
  <p>Best,
  Peter</p>