title: Cut function returns NA for intervals
body: <p>I am trying to use the cut function to create age intervals. Unfortunately, I receive NAs for values that match the lower end of the first break.</p>
  
  <p>For example:</p>
  
  <pre><code>AGE &lt;- sample(18:50, 100, replace = TRUE)
  AGE_GROUPS &lt;- cut(AGE, breaks = c(18, 27, 36, 45))
  DF &lt;- data.frame(AGE, AGE_GROUPS)
  </code></pre>
  
  <p>For all the values where AGE is 18 and above 45, I receive NA in the AGE_GROUPS variable. How can I make sure that the lowest bracket in AGE_GROUPS includes 18 and how can I make sure that the highest bracket includes all values >= 45?</p>