title: A matplotlib histogram matrix, using Pandas, with multiple categories overlaid
body: <p>I am trying to combine two approaches at creating histograms.</p>
  
  <pre><code>#Sample Data
  
  df = pd.DataFrame({'V1':[1,2,3,4,5,6], 
           'V2': [43,35,6,7,31,34], 
           'V3': [23,75,67,23,56,32],
           'V4': [23,45,67,63,56,32],
          'V5': [23,5,67,23,6,2],
          'V6': [23,78,67,76,56,2],
          'V7': [23,45,67,53,56,32],
          'V8': [5,5,5,5,5,5],
          'cat': ["A","B","C","A","B","B"],})
  </code></pre>
  
  <p>I am able to create a histogram matrix for each category using this code.</p>
  
  <pre><code> #1. Creating histogram matrix for each category 
  
  for i in df['cat'].unique():
      fig, ax = plt.subplots()
      df[df['cat']==i].hist(figsize=(20,20),ax =ax)
      fig.suptitle(i + " Feature-Class Relationships", fontsize = 20)
      fig.savefig('Histogram Matrix.png' %(i), dpi = 240)
  </code></pre>
  
  <p>This creates a separate histogram matrix for each category. However what I would like is for the categories to be overlaid on the same matrix. </p>
  
  <p>I am able to create an overlaid histogram using this approach: </p>
  
  <pre><code>#2. Overlaid histrogram for single variable
  
  fig, ax = plt.subplots()
  for i in df['cat'].unique():
      df[df['cat']==i]['V8'].hist(figsize=(12,8),ax =ax, alpha = 0.5, label = i)
  ax.legend()
  plt.show()
  </code></pre>
  
  <p>However this only creates a single overlaid image. I want to create an overlaid histogram for all of variables in the matrix i.e. all categories shown in the same matrix rather than a separate matrix for each category. 
  I have created the following code, which is a combination of the above two approaches, but it does not overlay each of the histogram matrices together and only the last plot is created. </p>
  
  <pre><code>#3. Combining approaches to create a matrix of overlaid histograms
  
  fig, ax = plt.subplots()
  for i in df['cat'].unique():
      df[df['cat']==i].hist(figsize=(12,8),ax =ax, alpha = 0.5, label = i)
  ax.legend()
  fig.savefig('Combined.png', dpi = 240)
  </code></pre>
  
  <p>Is what I am trying to do possible? </p>