title: How do read file by filtering rows based on a condition in R
body: <p>I am using R to reach csv. But i do not want whole dataset in memory as dataset is too large. But I need to read rows based on one column's category. </p>
  
  <p>I want to read only rows where col2 = 'A'</p>
  
  <p><strong>Example :</strong> 
  <strong>col1   col2   col 3</strong><br/>
  1      A      1000 <br/>
  2      B      2000 <br/>
  3      A      1000 <br/>
  4      A      2000 <br/>
  5      A      1000 <br/>
  6      B      2000 <br/>   </p>