title: Order facet_wrap plots by descending order
body: <p>I am trying to plot with <code>facet_wrap</code> that by default is ordering the plots alphabetically. However, the desired result would be to order it by a numerically descending column.</p>
  
  <p>Below is what I get:</p>
  
  <pre class="lang-r prettyprint-override"><code>library(tidyverse)
  
  M &lt;- data.frame(
      A = LETTERS[1:10],
      B = round(rnorm(10,200,50)), 
      C = letters[15:24]
    )
  
  ggplot(M, aes(A, B)) + 
      geom_bar(stat = "identity") + 
      facet_wrap(~C)
  </code></pre>
  
  <p>Instead, I am looking to get the plots ordered by column B descending</p>
  
  <pre class="lang-r prettyprint-override"><code>arrange(M, desc(B)) %&gt;%
      ggplot(aes(A, B)) + 
      geom_bar(stat = "identity") + 
      facet_wrap(~C)   ## need it ordered by B
  </code></pre>
  
  <p>I know one approach is to change the levels but I don´t know where in the sequence I can make it and how.</p>