title: Matplotlib plotting an undefined number of axes
body: <p>I am reading an excel sheet and generating a numpy array (data_array)
  In this array each row is a different group (for example: dogs, cats, birds, insects, etc... the number of items will depend on each excel sheet)
  The columns are fixed to 9 elements for each group (age, color, etc)</p>
  
  <p>Now I can graph plot each row. In this example I am only plotting the element 7 of the data_Array.</p>
  
  <pre><code>fig, ax = plt.subplots()
  x,y = data_array.shape
  
  ind = np.arange(y)  
  width = 1
  
  rects = ax.bar(ind, data_array[7], width, color='r')
  
  plt.xticks(ind, names, rotation=90)
  plt.ylabel('Area')
  plt.title('Normalized IS')          
  plt.show()
  </code></pre>
  
  <p>I could write:</p>
  
  <pre><code>rects1 = ax.bar(ind, data_array[1], width, color='r')
  rects2 = ax.bar(ind, data_array[2], width, color='r')
  .
  .
  .
  rectsx = ax.bar(ind, data_array[x], width, color='r')
  </code></pre>
  
  <p>Then I could plot all of them in the same chart.
  However, each excel I am reading have a different x number of elements.</p>
  
  <p>I thought about genereting them using:</p>
  
  <pre><code>for i in range(x):
      rects[i] = ax.bar(ind, data_array[i], width, color='r') 
  </code></pre>
  
  <p>but I got an error message.</p>
  
  <blockquote>
    <p>Traceback (most recent call last):</p>
    
    <p>File "", line 1, in 
        rects[1]=ax.bar(ind, data_array[7], width, color='r') NameError: name 'rects' is not defined</p>
  </blockquote>
  
  <p>How to generate each ax.bar?</p>