title: Plotting asymmetric error bars for a single point using errorbar
body: <p>Goal: To plot asymmetric x error bars for a single point using errorbar. I want to display the inter quartile range (IQR) for a data set. </p>
  
  <p>Code:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  y = 1.0
  data = np.random.rand(100)
  
  median = np.median(data)
  upper_quartile = np.percentile(data, 75)
  lower_quartile = np.percentile(data, 25)
  IQR = upper_quartile - lower_quartile
  
  plt.errorbar(median, y, xerr=[lower_quartile ,upper_quartile], fmt='k--')
  
  plt.savefig('IQR.eps')
  plt.show()
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "IQR.py", line 15, in &lt;module&gt;
      plt.errorbar(median, y, xerr=[0.5,0.75], fmt='k--')
    File "/usr/lib/pymodules/python2.7/matplotlib/pyplot.py", line 2251, in errorbar
      ret = ax.errorbar(x, y, yerr, xerr, fmt, ecolor, elinewidth, capsize, barsabove, lolims, uplims, xlolims, xuplims, **kwargs)
    File "/usr/lib/pymodules/python2.7/matplotlib/axes.py", line 5327, in errorbar
      in cbook.safezip(x,xerr)]
    File "/usr/lib/pymodules/python2.7/matplotlib/cbook.py", line 1294, in safezip
      raise ValueError(_safezip_msg % (Nx, i+1, len(arg)))
  ValueError: In safezip, len(args[0])=1 but len(args[1])=2
  </code></pre>
  
  <p>My issue is that I am unable to create asymmetric error bars for a single point, where the point will represent the mean and the upper and lower limits of the error bars will be the upper and lower quartile.</p>