title: ggplot, facets, and scale labelling
body: <p>I am producing a facet chart like this</p>
  <pre><code>suppressPackageStartupMessages({
    library(tidyverse)
    library(scales)
  })
  
  set.seed(123456)
  test_df &lt;-
    tibble(t=1:10,
           x=100+runif(10,-10,10),
           y=10+runif(10,-4,4),
           p=y/x)
  
  test_df |&gt;
    pivot_longer(cols=x:p,
                 names_to = &quot;var&quot;,
                 values_to = &quot;value&quot;) |&gt;
    mutate(var=factor(var,levels=c(&quot;x&quot;,&quot;y&quot;,&quot;p&quot;))) -&gt;
  test_df_long
  
  test_df_long |&gt;
    ggplot(aes(x=t,y=value)) +
    geom_line() +
    scale_y_continuous(limits=c(0,NA)) +
    facet_wrap(vars(var),ncol=1,
               scales = &quot;free_y&quot;)
  </code></pre>
  <p><a href="https://i.stack.imgur.com/naDpN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/naDpN.png" alt="enter image description here" /></a></p>
  <p>I would like to change the formatting of the labels for the p facet to percent.</p>
  <p>I have not found a way to use different labelling functions to different facets.</p>
  <p>Can it be done?</p>