title: Using mutate and starts_with
body: <p>I would like to change the value of certain variables depending on whether they start with a certain string-sequence.</p>
  
  <p>Example:</p>
  
  <pre><code>df &lt;- data.frame(var1 = c("12345", "12345", "12345", "23456", "23456"))
  df %&gt;% mutate(var2 = ifelse(starts_with("123"), "ok", "not ok"))
  </code></pre>
  
  <p>All values starting with "123" should be changed into "ok". How can I combine <code>starts_with()</code> with <code>mutate()</code>?</p>
  
  <p>Thanks!</p>