title: Changing labels on a facet plot
body: <p>I currently have a facet plot where i wish to change the heading of each facet to a new name. Does anyone know how to do this?</p>
  <pre><code>#data snipet
   Substation       Date cluster  Time     Value  weekday 
  1     511016 2013-01-17       1 00:00 0.6215941 Thursday       
  2     511029 2013-01-17       1 00:00 0.5677445 Thursday       
  3     511030 2013-01-17       1 00:00 0.6065458 Thursday       
  4     511033 2013-01-08       2 00:00 0.3090885  Tuesday       
  5     511034 2013-01-17       1 00:00 0.5263230 Thursday       
  6     511035 2013-01-17       1 00:00 0.5267718 Thursday       
  
  
  
  #current code
  
  ggplot(substation_average_long, aes(Time, Value, group = Substation, colour = cluster)) +
    geom_line(colour = 'grey') +
    facet_wrap(.~cluster) +
    ylab('Substation power output') +
    ggtitle('Substation power output by cluster') +
    theme(plot.title = element_text(hjust = 0.5, face = 'bold'))
  </code></pre>
  <p><a href="https://i.stack.imgur.com/VgGZU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/VgGZU.png" alt="enter image description here" /></a></p>
  <p>So i with to change 1 to 'cluster 1',  2 to 'cluster 2' and so on</p>