title: changing ggplot2::facet_wrap title from the default
body: <p>Is there any possible way to change the labels for the facet_wrap variable, as displayed below. So, for example, instead of <code>cyl: 4</code>, <code>cyl: 6</code>, <code>cyl: 8</code>, I want it to read <code>condition: 4</code>, <code>condition: 6</code>, <code>condition: 8</code>. Of course, I can just do this by renaming the variable, but that's not what I want. This is a much simpler version of a custom function where I can't just rename a variable anyway I like. </p>
  
  <p>Another way to put this is, do I have any freedom to label the <code>facet_wrap</code> anyway I like? Kinda like how <code>x</code> aesthetic variable in <code>ggplot2</code> can have some name (e.g. <code>cyl</code>) in the dataframe (<code>mtcars</code>), but I can still replace it with my own name using <code>labs(x = "cylinder")</code>). I want to have something similar for <code>facet_wrap</code>.  </p>
  
  
  
  <pre class="lang-r prettyprint-override"><code>library(dplyr)
  library(datasets)
  library(ggplot2)
  data(mtcars)
  
  # creating a dataframe
  df &lt;- dplyr::group_by(mtcars, .dots = c('cyl', 'am')) %&gt;%
    dplyr::summarize(counts = n()) %&gt;%
    dplyr::mutate(perc = (counts / sum(counts)) * 100) %&gt;%
    dplyr::arrange(desc(perc))
  
  # preparing the plot
  ggplot2::ggplot(df, aes('', counts)) +
    geom_col(
      position = 'fill',
      color = 'black',
      width = 1,
      aes(fill = factor(am))
    ) +
    facet_wrap(~cyl, labeller = "label_both") + # faceting by `cyl` variable
    geom_label(
      aes(label = paste0(round(perc), "%"), group = factor(am)),
      position = position_fill(vjust = 0.5),
      color = 'black',
      size = 5,
      show.legend = FALSE
    ) +
    coord_polar(theta = "y")
  </code></pre>
  
  <p><img src="https://i.imgur.com/bsVLUYB.png" alt=""></p>
  
  <p>Created on 2018-02-19 by the <a href="http://reprex.tidyverse.org" rel="noreferrer">reprex package</a> (v0.2.0).</p>