title: R + ggplot2 => add labels on facet pie chart
body: <p>I want to add data labels on faceted pie char.<br>
  Maybe someone can can help me.</p>
  
  <p>My data:  </p>
  
  <pre><code>year &lt;- c(1,2,1,2,1,2)
  prod &lt;- c(1,1,2,2,3,3)
  quantity &lt;- c(33,50,33,25,34,25)
  
  df &lt;- data.frame(year, prod, quantity)
  rm(year, prod, quantity)
  </code></pre>
  
  <p>Code:</p>
  
  <pre><code>library(ggplot2)
  
  # center's calculated by hand
  centr2 &lt;- c(16, 25, 49, 62.5, 81, 87.5)
  
  ggplot(data=df, aes(x=factor(1), y=quantity, fill=factor(prod))) +
      geom_bar(stat="identity") +
      geom_text(aes(x= factor(1), y=centr2, label = df$quantity), size=10) +
      facet_grid(facets = .~year, labeller = label_value) +
      coord_polar(theta = "y")
  </code></pre>
  
  <p>And my result is:</p>
  
  <p><img src="https://i.stack.imgur.com/Po0ov.jpg" alt="pie char"></p>
  
  <p>If I remove coord_polar(theta = "y"), I will have the following plot:</p>
  
  <p><img src="https://i.stack.imgur.com/mEHRv.jpg" alt="bar plot"></p>
  
  <p>And now it is clear for me, why my data labels did not match.<br>
  But I don't know how to fix it.   </p>
  
  <p>I read:<br>
  1. <a href="https://stackoverflow.com/questions/20443467/place-labels-on-pie-chart">Place labels on Pie Chart</a><br>
  2. <a href="https://stackoverflow.com/questions/22896696/add-text-to-ggplot-with-facetted-densities">Add text to ggplot with facetted densities</a><br>
  3. <a href="https://stackoverflow.com/questions/8952077/pie-plot-getting-its-text-on-top-of-each-other">Pie plot getting its text on top of each other</a></p>
  
  <p>But didn't find the answer.  </p>