title: R: Error: Objects of type numeric not supported by autoplot
body: <p>Below function gives error:</p>
  
  <pre><code>autoplot(melsyd[,'Economy.Class']) +
    ggtitle("Economy class passengers: Melbourne-Sydney") +
    xlab("Year") +
    ylab("Thousands")
  
  Error: Objects of type numeric not supported by autoplot.
  </code></pre>
  
  <p>Brief about the dataframe:</p>
  
  <pre><code> melsyd = read.csv("http://course1.winona.edu/bdeppa/FIN%20335/Datasets/MelSyd.csv")
  
  &gt; head(melsyd,2)
    First.Class Business.Class Economy.Class
  1       1.912             NA        20.167
  2       1.848             NA        20.161
  </code></pre>
  
  <p>Please help. I am trying to plot Economy class values against time</p>