title: multiple scatter plots with matplotlib and strings on the x-axis.
body: <p>I'm trying to make three scatter plots in one figure. I tried it this way.</p>
  
  <p>Do an import first. </p>
  
  <pre><code>import matplotlib.pyplot as plt 
  </code></pre>
  
  <p>Define the variables and make one figure that contains three scatter plots. </p>
  
  <pre><code>c_pop = [0.410, -0.094, -0.111, -0.106, -0.090, 0.070, -0.043, -0.181, 0.221]
  c_labels = ['ll120', 'll123', 'll124', 'll27', 'll28', 'll30', 'll446, n12', 'll447, n86', 'll471']
  pre_lo = [-0.493]
  post_lo = [0.145]
  lo_label = ['lo']
  
  fig = plt.figure()
  ax1 = fig.add_subplot(111)
  
  ax1.scatter(c_labels, c_pop, color='black')
  ax1.scatter(lo_label, pre_lo, color='green', label='pre-SNEP')
  ax1.scatter(lo_label, post_lo, color='red', label='post-SNEP')
  
  plt.show()
  </code></pre>
  
  <p>The error I get is: could not convert string to float: lo</p>
  
  <p>It seems like it tries to convert lo_label into something else. </p>
  
  <p>The code runs if I disable the first scatter plot and only run the second and the third. It also runs when I only run the first scatter plot and disable the second the third. </p>
  
  <p>What is going wrong? Is it possible to make three scatter plots in one plot with labels on the x-axis?</p>