title: How can I filter variables by a specific type
body: <p>Having the table below as an example, how can I filter only columns that are of type 'chr' ? For example, I would like to see a list of only string variables:<br>
  for example :
  Timber chr</p>
  
  <pre><code>dat &lt;- read.table(text = " Timber apcalc    admit       num
     pine        0        0         7
     pine        0        1         1
     oak         1        0         3
     olive       1        1         7
     olive       0        0         5
     oak         0        1         1
     pine        1        0         0
     pine        1        1         6", header = TRUE)
  </code></pre>