title: Matplotlib pyplot semilogy broken for specific data
body: <p>I am trying to display data on a semi-log scale using matplotlib.pyplot.semilogy but for some reason certain specific data will not display on a log scale.</p>
  
  <p>Here is the minimal example:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  x1 = np.linspace(0, 1, 50)
  y1 = np.linspace(0.1, 10, 50)
  
  x2 = [ 0.5, 0.69230769,  0.88461538,  1.07692308,  1.26923077,  1.46153846,
  1.65384615,  1.84615385,  2.03846154,  2.23076923,  2.42307692,  2.61538462,
  2.80769231,  3.,          3.19230769,  3.38461538,  3.57692308,  3.76923077,
  3.96153846,  4.15384615,  4.34615385,  4.53846154,  4.73076923,  4.92307692,
  5.11538462,  5.30769231,  5.5,         5.69230769,  5.88461538,  6.07692308,
  6.26923077,  6.46153846,  6.65384615,  6.84615385,  7.03846154,  7.23076923,
  7.42307692,  7.61538462,  7.80769231,  8.        ]
  
  y2 = [14.575361987617431, 13.085951334251263, 11.624204239934841, 11.042131295677322, 10.644970825480804,
  9.9236653345614503, 9.5062099711101915, 9.3283627736535824, 9.0534046482183932, 8.8134672834907359,
  8.4231263934928542, 8.42795792391086, 8.4456426949395116, 8.0627962362862267, 8.164485063139546,
  7.9551127994296023, 7.8244362249461439, 7.9030927230355665, 7.7181207757466472, 7.5995483354781648,
  7.5188031175401084, 7.5583740928502579, 7.5662853869793665, 7.437330171526578, 7.3623785273467872,
  7.3503413700294535, 7.375341864137301, 7.300590983871917, 7.2357339123237017, 7.1353470647499266,
  7.1784115809287599, 7.1576686293908374, 7.097654663701598, 6.9911420242692399, 7.0015210243972046,
  6.9017431583355604,6.9352210046151539, 6.8707305411431996, 6.7925239329688045, 6.7930737708109978]
  
  plt.figure(1)
  
  plt.subplot(2,1,1)
  # plt.plot(x1, y1, 'o-')
  plt.plot(x2, y2, 'o-')
  plt.title('Linear Scale')
  
  plt.subplot(2,1,2)
  # plt.semilogy(x1, y1, 'o-')
  plt.semilogy(x2, y2, 'o-')
  plt.title('Semi-Log Scale')
  
  plt.subplots_adjust(top=0.95, bottom=0.05, hspace = 0.25)
  
  plt.show()
  </code></pre>
  
  <p>Which outputs:
  <a href="https://i.stack.imgur.com/yIElb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/yIElb.png" alt="Y-axis not displaying log scale"></a></p>
  
  <p>But if I plot x1 and y1 instead it seems to work normally:</p>
  
  <p><a href="https://i.stack.imgur.com/DMRRo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DMRRo.png" alt="semilogy working normally"></a></p>
  
  <p>I'm not sure why this is, maybe there is a bug in semilogy? Does anyone know a workaround?</p>
  
  <p>I'm using matplotlib version 2.1.0 on python version 3.6.3</p>