title: Seaborn violin plot using arrays - Error: Neither the `x` nor `y` variable appears to be numeric
body: <p>I am trying to generate several violin plots in one, using seaborn. The dataframe 
  I use includes several categorical values in one column (to be used on the x-axis), with an array of values for each categorical value (to be used to create the violin plot for each categorical value). A small working example would be this:</p>
  
  <pre><code>foo = pd.DataFrame(columns =['Names','Values'])
  for i in range(10):
      foo.loc[i] = ['no'+str(i),np.random.normal(i,2,10)]
  </code></pre>
  
  <p>But when trying</p>
  
  <pre><code>sns.violinplot(x='Names', y='Values', data=foo)
  </code></pre>
  
  <p>I get the following error</p>
  
  <blockquote>
    <p>ValueError: Neither the <code>x</code> nor <code>y</code> variable appears to be numeric.</p>
  </blockquote>
  
  <p>Now I could be hacky and just separate the array across several rows as such:</p>
  
  <pre><code>foo = pd.DataFrame(columns =['Names','Values'])
  for i in range(3):
      bar = np.random.normal(i,2,10)
      for j,b in enumerate(bar):
          foo.loc[i*10+j] = ['no'+str(i),b]
  </code></pre>
  
  <p>which yields the plot I want:</p>
  
  <p><a href="https://i.stack.imgur.com/mkkcJ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/mkkcJ.png" alt="enter image description here"></a></p>
  
  <p>But I'm guessing there is a more simple solution to this, without needing to restructure my dataframe.</p>