title: Subsetting while reading in R
body: <p>I have a 5+ million rows in R with just 4 cols per row. One of the columns is the date when the data was collected. An example is</p>
  
  <pre><code>Date        PI   SSC    GC
  2/11/2013 0.52  0.89   4.2
  2/11/2013 0.56  0.45  12.0
  2/11/2013 0.49  0.89  13.1
  2/11/2013 0.59  0.47   4.8 
  2/11/2013 0.61  0.58  12.3
  </code></pre>
  
  <p>I would like to know if there is a way to read ONLY certain rows corresponding for certain dates, rather than having to read the 5 million rows and then subsetting. For example, all rows corresponding to the date 2/11/2013 (I do not know how many are in the file). Also, in case it's of any help, the class of the Date column is factor.</p>