title: Plot dataframe with datetime index
body: <pre><code>            is_avail   valu data_source
  2015-08-07     False  0.282    source_a
  2015-08-23     False  0.296    source_a
  2015-09-08     False  0.433    source_a
  2015-10-01      True  0.169    source_a
  2015-10-10      True  0.160    source_a
  2015-11-02     False  0.179    source_a
  2016-03-09     False  0.557    source_a
  2016-04-26     False  0.770    source_a
  2016-05-05     False  0.826    source_a
  2016-05-12     False  0.826    source_a
  2016-05-28     False  0.747    source_a
  2016-06-06     False  0.796    source_a
  2016-07-31     False  0.322    source_a
  2016-08-25      True  0.136    source_a
  2016-09-10     False  0.180    source_a
  2016-11-13     False  0.492    source_a
  2016-12-15      True  0.124    source_a
  2016-12-31     False  0.533    source_a
  2017-03-28     False  0.524    source_a
  2015-06-27      True  0.038    source_b
  2015-07-30      True  0.035    source_b
  2015-08-06     False  0.205    source_b
  2015-08-09     False  0.241    source_b
  2015-08-16      True  0.025    source_b
  2015-08-19      True  0.092    source_b
  2015-08-26     False  0.264    source_b
  2015-08-29     False  0.312    source_b
  </code></pre>
  
  <p>I want to plot the <code>valu</code> column in the dataframe above, with separate line plots for <code>source_a</code> rows and <code>source_b</code> rows and separate colors when <code>is_avail</code> is True or False. Currently, I am doing this:</p>
  
  <pre><code>df['valu'].plot()
  </code></pre>
  
  <p>However, this shows everything as a single line plot. How to get to the objective above?</p>