title: R - ggplot2 - geom_line - Get rid of straight line for missing values
body: <p>I have data that I am trying to plot.  I have several variables that range from the years 1880-2012.  I have one observation per year.  But sometimes a variable does not have an observation for a number of years.  For example, it may have an observation from 1880-1888, but then not from 1889-1955 and then from 1956-2012.  I would like ggplot2 + geom_line to not have anything in the missing years (1889-1955).  But it connects 1888 and 1956 with a straight line.  Is there anything I can do to remove this line?  I am using the ggplot function.</p>
  
  <p>Unrelated question, but is there a way to get ggplot to not sort my variable names in the legend alphabetically? I have code like this:</p>
  
  <pre><code>ggplot(dataFrame, aes(Year, value, colour=Name)) + geom_line()
  </code></pre>
  
  <p>Or to add numbers in front of the variable names (Name1, ..., Name10) to the legend. For example, 
  1. Name1
  2. Name2
  ...
  10. Name10</p>