title: Cannot cast array data from dtype('O') to dtype('float64') according to the rule 'safe'
body: <p>When running my Tukey test, it gives me this error:</p>
  
  <blockquote>
    <p>Cannot cast array data from dtype('O') to dtype('float64') according
    to the rule 'safe'</p>
  </blockquote>
  
  <p>My Dataframe Head Output:</p>
  
  <pre><code>    Group    Score
  3   A        1.91
  4   B        1.7
  5   C        1.69
  6   D        1.68
  7   E        1.49
  </code></pre>
  
  <p>My Tukey Test Code:</p>
  
  <pre><code>from statsmodels.stats.multicomp import pairwise_tukeyhsd
  from statsmodels.stats.multicomp import MultiComparison
  
  mc = MultiComparison(df['Score'], df['Group'])
  result = mc.tukeyhsd()
  
  print(result)
  print(mc.groupsunique)
  
  
  &gt; TypeError Traceback (most recent call
  &gt; last) &lt;ipython-input-10-705a07612b72&gt; in &lt;module&gt;()
  &gt;       1 mc = MultiComparison(df['Score'], df['Group'])
  &gt; ----&gt; 2 result = mc.tukeyhsd()
  &gt;       3 
  &gt;       4 print(result)
  &gt;       5 print(mc.groupsunique)
  &gt; 
  &gt; /usr/local/lib/python3.6/dist-packages/statsmodels/sandbox/stats/multicomp.py
  &gt; in tukeyhsd(self, alpha)
  &gt;     964         self.groupstats = GroupsStats(
  &gt;     965                             np.column_stack([self.data, self.groupintlab]),
  &gt; --&gt; 966                             useranks=False)
  &gt;     967 
  &gt;     968         gmeans = self.groupstats.groupmean
  &gt; 
  &gt; /usr/local/lib/python3.6/dist-packages/statsmodels/sandbox/stats/multicomp.py
  &gt; in __init__(self, x, useranks, uni, intlab)
  &gt;     535 
  &gt;     536         #temporary until separated and made all lazy
  &gt; --&gt; 537         self.runbasic(useranks=useranks)
  &gt;     538 
  &gt;     539 
  &gt; 
  &gt; /usr/local/lib/python3.6/dist-packages/statsmodels/sandbox/stats/multicomp.py
  &gt; in runbasic(self, useranks)
  &gt;     569         else:
  &gt;     570             self.xx = x[:,0]
  &gt; --&gt; 571         self.groupsum = groupranksum = np.bincount(self.intlab, weights=self.xx)
  &gt;     572         #print('groupranksum', groupranksum, groupranksum.shape, self.groupnobs.shape
  &gt;     573         # start at 1 for stats.rankdata :
  &gt; 
  &gt; TypeError: Cannot cast array data from dtype('O') to dtype('float64')
  &gt; according to the rule 'safe'
  </code></pre>
  
  <p>Does anyone know what this means?</p>