title: Mutate, across, and case_when
body: <p>I am having some trouble getting mutate, across, and case_when to function properly, I've recreated a simple version of my problem here:</p>
  <pre><code>a &lt;- c(1:10)
  b &lt;- c(2:11)
  c &lt;- c(3:12)
  
  test &lt;- tibble(a, b, c)
  
  # A tibble: 10 x 3
         a     b     c
     &lt;int&gt; &lt;int&gt; &lt;int&gt;
   1     1     2     3
   2     2     3     4
   3     3     4     5
   4     4     5     6
   5     5     6     7
   6     6     7     8
   7     7     8     9
   8     8     9    10
   9     9    10    11
  10    10    11    12
  </code></pre>
  <p>My goal is to replace all of the 3's with 4's, and keep everything else the same. I have the following code:</p>
  <pre><code>test_1 &lt;- 
    test %&gt;% 
    mutate(across(a:c, ~ case_when(. == 3 ~ 4)))
  
  # A tibble: 10 x 3
         a     b     c
     &lt;dbl&gt; &lt;dbl&gt; &lt;dbl&gt;
   1    NA    NA     4
   2    NA     4    NA
   3     4    NA    NA
   4    NA    NA    NA
   5    NA    NA    NA
   6    NA    NA    NA
   7    NA    NA    NA
   8    NA    NA    NA
   9    NA    NA    NA
  10    NA    NA    NA
  </code></pre>
  <p>It's close but I get NA values where I want to maintain the value in the original tibble. <strong>How do I maintain the original values using the mutate across structure?</strong></p>
  <p>Thank you in advance!</p>