title: Remove all rows where length of string is more than n
body: <p>I have a dataframe <code>m</code> and I want to remove all the rows where the <code>f_name</code> column has an entry greater than 3. I assume I can use something similar to </p>
  
  <pre><code>m &lt;- m[-grep("nchar(m$f_name)&gt;3", m$f_name]
  </code></pre>