title: Create categories by comparing a numeric column with a fixed value
body: <p>Consider the <code>iris</code> data:</p>
  <pre><code> iris 
          Sepal.Length Sepal.Width Petal.Length Petal.Width    Species
      1            5.1         3.5          1.4         0.2     setosa
      2            4.9         3.0          1.4         0.2     setosa
      3            4.7         3.2          1.3         0.2     setosa
      4            4.6         3.1          1.5         0.2     setosa
      5            5.0         3.6          1.4         0.2     setosa
      6            5.4         3.9          1.7         0.4     setosa
      7            4.6         3.4          1.4         0.3     setosa
  </code></pre>
  <p>I want to create a new column based on a comparison of the values in variable <code>Sepal.Length</code> with a fixed limit / cut-off, e.g. check if the values are larger or smaller than 5:</p>
  <p><code>if Sepal.Length &gt;= 5 assign &quot;UP&quot; else assign &quot;DOWN&quot;</code> to a new column &quot;Regulation&quot;.</p>
  <p>What's the way to do that?</p>