title: Add values in column based on another column
body: <p>From </p>
  
  <pre><code>x &lt;- read.csv("stats.csv", header = TRUE)
  </code></pre>
  
  <p>I have two columns:</p>
  
  <pre><code>Gender   Score
  male     20
  female   25
  male     10
  female   10
  </code></pre>
  
  <p>How do I add the total Score for just males for example?</p>