title: Error: "zero-length arrow is of indeterminate angle and so skipped"
body: <p>This is my first time posting here so I'll do my best; I'm trying to add error bars to a plot but I'm getting the following error:</p>
  <pre><code>Warning messages:
  1: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  2: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  3: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  4: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  5: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  6: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  7: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  8: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  9: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  10: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  11: In arrows(x0 = pen$l, y0 = pen$per - pen$error, x1 = pen$l,  ... :
    zero-length arrow is of indeterminate angle and so skipped
  There were 22 warnings (use warnings() to see them)
  </code></pre>
  <p>This is the code I'm using:</p>
  <pre><code>pen=read.csv(&quot;datosalt.csv&quot;,header=T)
  plot(pen$l,pen$per,pch=19)
  arrows(x0=pen$l,y0=pen$per-pen$error,x1=pen$l,y1=pen$per-pen$error,code=3,length=0.02,angle=90)
  </code></pre>
  <p>And this is my dataframe (datosalt.csv):</p>
  <pre><code>per,error,l
  0.78,0.06,15
  1,0.05,25
  1.21,0.06,35
  1.37,0.07,45
  1.49,0.03,55
  1.62,0.03,65
  1.62,0.03,65
  1.74,0.03,75
  1.88,0.06,85
  1.88,0.06,85
  1.96,0.08,95
  </code></pre>
  <p>There <em>should</em> be nothing wrong with them since the numbers in my dataframe make sense and the code was written by my proffesor, but it shows me those warnings and doesn't add the error bars I need. I haven't been able to find anything online since this seems to be a problem specific to each code, plus I'm pretty new to coding altogether, so if anyone can point me in the right direction I'd greatly appreciate it.</p>