title: Using replace_na with across in mutate
body: <p>I am trying to replace NA in a subset of columns and I want to use tidyverse/dplyr syntax.
  dplyr v1.0.2</p>
  <p>In the following, I want only to replace the NAs with 999 in columns ab,ac but not in ads</p>
  <pre><code>tbf &lt;- tibble( ab = c(1,3,NA), ac = c(23,NA,33), d = c(22,22,NA), ads = c('ds', NA, &quot;dwe&quot;))
  tbf %&gt;% mutate(across(starts_with('a') &amp; where(is.numeric)), ~replace_na(999))
  </code></pre>
  <p>does not seem to work.</p>
  <p>I tried <code>~replace_na(.x,999)</code> too. That didn't work either.</p>
  <p>Any help is appreciated.</p>