title: How to use mutate_at with ifelse
body: <p>I'm trying to use the <code>mutate_at</code> function with <code>ifelse</code> but it does not work.</p>
  <p>As an example here is what I want to achieve</p>
  <pre><code>data &lt;- data.frame(
    A = c(1, 2, 3, 4),
    B = c(2, 3, 4, 1),
    C = c(4, 1, 9, 0)
  )
  
  data %&gt;%
    mutate(A = ifelse(A == 4, 1, A)) %&gt;%
    mutate(B = ifelse(B == 4, 1, B))
  </code></pre>
  <p>by using the <code>mutate_at</code> function. Any help would be appreciated.</p>