title: How to extract data from a data table in R
body: <p>I am asking a pretty basic question:
  how to pull out &quot;Female&quot; data from this table
  and calculating average number for &quot;Females&quot; using R.
  Two columns 1. sex   2. height</p>
  <pre><code>sex    height
  Male   75.00000
  Male   70.00000
  Female 65.00000
  Female 66.00000
  </code></pre>
  <p>Thanks a lot!</p>