title: Selecting DataFrame slices by date string
body: <p>I have a DataFrame which is loaded like so</p>
  
  <pre><code>        minData = pd.read_csv(
                  currentSymbol["fullpath"],
                  header = None,
                  names = ['Date', 'Time', 'Open', 'High', 'Low', 'Close', 'Volume', 'Split Factor', 'Earnings', 'Dividends'], 
                  parse_dates = [["Date", "Time"]],
                  date_parser = lambda x : datetime.datetime.strptime(x, '%Y%m%d %H%M'), 
                  index_col = "Date_Time",
                  sep=' ')
  </code></pre>
  
  <p>The data looks like this</p>
  
  <pre><code>&gt;&gt;&gt; minData.index
  &lt;class 'pandas.tseries.index.DatetimeIndex'&gt;
  [1998-01-02 09:30:00, ..., 2013-12-09 16:00:00]
  Length: 1373036, Freq: None, Timezone: None
  &gt;&gt;&gt; 
  
  &gt;&gt;&gt; minData.head(5)
                          Open     High      Low    Close   Volume  \
  Date_Time                                                          
  1998-01-02 09:30:00  8.70630  8.70630  8.70630  8.70630   420.73   
  1998-01-02 09:35:00  8.82514  8.82514  8.82514  8.82514   420.73   
  1998-01-02 09:42:00  8.79424  8.79424  8.79424  8.79424   420.73   
  1998-01-02 09:43:00  8.76572  8.76572  8.76572  8.76572  1262.19   
  1998-01-02 09:44:00  8.76572  8.76572  8.76572  8.76572   420.73   
  
                       Split Factor  Earnings  Dividends  Active  
  Date_Time                                                       
  1998-01-02 09:30:00             4         0          0     NaN  
  1998-01-02 09:35:00             4         0          0     NaN  
  1998-01-02 09:42:00             4         0          0     NaN  
  1998-01-02 09:43:00             4         0          0     NaN  
  1998-01-02 09:44:00             4         0          0     NaN  
  
  [5 rows x 9 columns]
  </code></pre>
  
  <p>I can select rows from my DataFrame like this</p>
  
  <pre><code>&gt;&gt;&gt; minData["2004-12-20"]
                          Open     High      Low    Close     Volume  \
  Date_Time                                                            
  2004-12-20 09:30:00  35.8574  35.9373  35.8025  35.9273  154112.00   
  2004-12-20 09:31:00  35.8924  35.9174  35.8824  35.8874   17021.50   
  2004-12-20 09:32:00  35.8874  35.8924  35.8824  35.8824   17079.50   
  2004-12-20 09:33:00  35.8874  35.9423  35.8724  35.9373   32491.50   
  2004-12-20 09:34:00  35.9373  36.0023  35.9174  36.0023   40096.40   
  2004-12-20 09:35:00  35.9923  36.2071  35.9923  36.1471   67088.90   
  ...
  </code></pre>
  
  <p>I have dates that look like this (read from a different file)</p>
  
  <pre><code>&gt;&gt;&gt; ts
  Timestamp('2004-12-20 00:00:00', tz=None)
  &gt;&gt;&gt; 
  </code></pre>
  
  <p>I want to set the 'Active' col to True for all minutes on this day.</p>
  
  <p>I can do this with this</p>
  
  <pre><code>minData.loc['2004-12-20',"Active"] = True
  </code></pre>
  
  <p>And I can do the same thing with my TimeStamp date with this crazy piece of code </p>
  
  <pre><code>minData.loc[str(ts.year) + "-" + str(ts.month) + "-" + str(ts.day),"Active"] = True
  </code></pre>
  
  <p>Yes, thats creating a string from the TimeStamp object!</p>
  
  <p>I know there must be a better way to do this..</p>