title: Why is substr function slow with dataframes?
body: <p>I am working on extracting substrings from a dataframe faving 700,000 rows. </p>
  
  <p>For example, lets say I have a variable <code>ord</code> which is a dataframe of size 1 X 700,000.
  I am using <code>substr(ord[, 1], 23, 36)</code> but it is very slow. Can somebody suggest some other method or improvements?</p>