title: Plotting two columns against each other omitting missing values
body: <p>This is my dataframe using dput():</p>
  
  <pre><code>structure(list(Year = 1900:1903, Top.10..income.share = structure(c(82L, 
  81L, 76L, 75L), .Label = c("", "30,3", "30,65", "30,8", "31,3", 
  "31,37", "31,38", "31,4", "31,5", "31,51", "31,52", "31,55", 
  "31,62", "31,64", "31,66", "31,67", "31,69", "31,75", "31,77", 
  "31,8", "31,81", "31,82", "31,85", "31,9", "31,98", "32,01", 
  "32,03", "32,04", "32,05", "32,07", "32,11", "32,12", "32,2", 
  "32,35", "32,36", "32,42", "32,43", "32,44", "32,5", "32,62", 
  "32,64", "32,67", "32,72", "32,82", "32,87", "33,02", "33,22", 
  "33,4", "33,69", "33,72", "33,76", "33,87", "33,95", "34,25", 
  "34,4", "34,57", "34,62", "34,71", "35,49", "36,3", "36,48", 
  "37,26", "37,3", "37,73", "37,77", "37,78", "37,84", "37,92", 
  "38,01", "38,1", "38,2", "38,38", "38,4", "38,47", "38,52", "38,59", 
  "38,6", "38,63", "38,84", "38,91", "38,99", "39,13", "39,31", 
  "39,48", "39,6", "39,82", "39,9", "40,29", "40,54", "40,59", 
  "40,75", "41,02", "41,16", "41,52", "41,73", "41,98", "42,12", 
  "42,23", "42,36", "42,67", "42,76", "42,86", "42,95", "43", "43,07", 
  "43,11", "43,26", "43,35", "43,39", "43,64", "43,76", "44,07", 
  "44,17", "44,4", "44,43", "44,57", "44,67", "44,77", "44,94", 
  "45,03", "45,16", "45,47", "45,5", "45,67", "45,96", "46,09", 
  "46,3", "46,35", "46,54"), class = "factor")), .Names = c("Year", 
  "Top.10..income.share"), row.names = c(NA, 4L), class = "data.frame")
  </code></pre>
  
  <p>My sessionInfo():  </p>
  
  <pre><code>R version 2.15.0 (2012-03-30)
  Platform: x86_64-apple-darwin9.8.0/x86_64 (64-bit)
  
  locale:
  [1] de_DE.UTF-8/de_DE.UTF-8/de_DE.UTF-8/C/de_DE.UTF-8/de_DE.UTF-8
  
  attached base packages:
  [1] stats     graphics  grDevices utils     datasets  methods   base     
  
  loaded via a namespace (and not attached):
  [1] rstudio_0.97.248 tools_2.15.0  
  </code></pre>
  
  <p>What I want to do is to plot the Year column against the Top10 column.<br>
  But since there are a quite a few missing values the graph looks pretty awful.<br>
  Here is the code I wrote to plot this so far.  </p>
  
  <pre><code>require(stats)
  
  tid_a = read.csv("tid-a.csv", header=TRUE, sep=";")
  germany &lt;- tid_a[1:111, ]
  usa &lt;- tid_a[112:210, ]
  
  germany_year &lt;- germany[, 2]
  germany_top10 &lt;- na.omit(germany[, 3])
  
  plot(germany_year, germany_top10, type="l")
  </code></pre>
  
  <p>I've tried a few examples I found online to omit the missing values, but I'm a noob and can't get it to work.  </p>