title: R qqplot argument "y" is missing error
body: <p>I am relatively new to R and I am struggling with a error messages related to <code>qqplot</code>.  Some sample data are at the bottom.  I am trying to do a <code>qqplot</code> on some azimuth data, i.e. like compass directions.  I've looked around here and the <code>?qqplot</code> R documentation, but I don't see a solution I can understand in either.  I don't understand the syntax for the function or the format the data are supposed to be in, or probably both.  I First I tried loading the data as a single column of values, i.e. just the "Azimuth" column.</p>
  
  <pre><code>azimuth &lt;- read.csv(file.choose(), header=TRUE)
  qqplot(azimuth$Azimuth)
  </code></pre>
  
  <p>returns the following error,</p>
  
  <pre><code>Error in sort(y) : argument "y" is missing, with no default
  </code></pre>
  
  <p>Then I tried including the corresponding dip angles along with the azimuth data and received the same error.  I also tried,</p>
  
  <pre><code>qqnorm(azimuth)
  </code></pre>
  
  <p>but this returned the following error,</p>
  
  <pre><code>Error in xy.coords(x, y, xlabel, ylabel, log) : 
  'x' and 'y' lengths differ
  </code></pre>
  
  <p>Dataframe "azimuth":</p>
  
  <pre><code>    Azimuth        Altitude
  23.33211466    -6.561729793
  31.51267873     4.801537153
  29.04577711      5.24504954
  23.63450905     14.03342708
  29.12535459     7.224141678
  20.76972007     47.95686329
  54.89253987     4.837417689
  56.57958227     13.12587996
  13.09845182    -7.417776178
  26.45155154     31.83546988
  29.15718557     25.47767069
  28.09084746     14.61603384
  28.93436865    -1.641785416
  28.77521371     17.30536039
  29.58690392    -2.202076058
  0.779859221     12.92044019
   27.1359178     12.20305106
  23.57084707     11.97925859
  28.99803063     3.931326877
  </code></pre>
  
  <p><code>dput()</code> version:</p>
  
  <pre><code>azimuth &lt;- 
  structure(list(Azimuth = c(23.33211466, 31.51267873, 29.04577711, 
  23.63450905, 29.12535459, 20.76972007, 54.89253987, 56.57958227, 
  13.09845182, 26.45155154, 29.15718557, 28.09084746, 28.93436865, 
  28.77521371, 29.58690392, 0.779859221, 27.1359178, 23.57084707, 
  28.99803063), Altitude = c(-6.561729793, 4.801537153, 5.24504954, 
  14.03342708, 7.224141678, 47.95686329, 4.837417689, 13.12587996, 
  -7.417776178, 31.83546988, 25.47767069, 14.61603384, -1.641785416, 
  17.30536039, -2.202076058, 12.92044019, 12.20305106, 11.97925859, 
  3.931326877)), .Names = c("Azimuth", "Altitude"), class = "data.frame", row.names = c(NA, -19L))
  </code></pre>