title: How do I plot hours and minutes when they are in different pandas columns?
body: <p>I have a pandas' dataframe like:</p>
  <pre><code> hour   minute     cnt
      0        0  904890
      0       30  880374
      1        0  848198
      1       30  816488
      2        0  791761
  </code></pre>
  <p>I would like to plot <code>cnt</code> using <code>minute</code> as minor ticks, and <code>hour</code> as major tick in matplotlib. I've tried several things but they didn't work. Here's one:</p>
  <pre class="lang-py prettyprint-override"><code>fig, ax = plt.subplots(figsize=(8,5))
  df.plot(kind='line', y='cnt', ax=ax)
  ax.set_xticks(df['minute'])
  ax.set_xticklabels(df['minute'])
  </code></pre>
  <p>I'd like my x-axis to look like</p>
  <pre><code>|---+---+---+---+---+---+---+---|
  0   15  30  45  0   30  45  0   15
  0               1           2   ...
  </code></pre>
  <p>Thanks.</p>