title: r - ggplot2 scale_x_discrete does not show the values, missing values warning
body: <p>I have a data frame;</p>
  
  <p>![temp][1]</p>
  
  <pre><code>First row are headers:
  
   LAYER, Number, Share %
   Between 100ms - 200ms , 132 , 4.66%
   Between 15ms - 30 ms , 475 , 16.8%
   Between 200ms - 300ms , 8 , 0.282%
   Between 300ms - 400ms , 1 , 0.0353%
   Between 30ms - 50 ms , 1329 , 46.9%
   Between 400ms - 500ms , 4 , 0.141%
   Between 500ms - 600ms , 2 , 0.0706%
   Between 50ms - 100ms , 863 , 30.5%
   Greater Than 600ms , 1 , 0.0353%
   Less Than 15ms , 17 , 0.6%) 
  </code></pre>
  
  <p>I am drawing the bar plot of it as:</p>
  
  <pre><code>myplot &lt;- ggplot(temp, aes(as.factor(temp$layer), temp$n, label = temp$yuzde)) + xlab("") + ylab("# of SDNNs") + 
  geom_bar(stat = "identity", width = 0.6, position = "dodge") +  
  theme(axis.text=element_text(size=8), axis.title = element_text(size=8,face="bold"), axis.text.x = element_text(angle = 90, hjust = 1)) + 
  scale_x_discrete(limits=c("Less Than 15ms", "Betwenn 15ms - 30 ms", "Betwenn 30ms - 50 ms", "Betwenn 50ms - 100 ms","Betwenn 100ms - 200 ms", "Betwenn 200ms - 300 ms","Betwenn 300ms - 400 ms", "Betwenn 400ms - 500 ms","Betwenn 500ms - 600 ms", "Greater Than 600ms")) +
  geom_label()
  </code></pre>
  
  <p>And the graphs comes as;</p>
  
  <p><img src="https://i.stack.imgur.com/rEOnl.png" alt="ggplot"></p>
  
  <p>but when I exclude <code>scale_x_discrete</code>, everything is normal ! 
  Like this;</p>
  
  <p>[ggplot normal][3]</p>
  
  <p>But I want to have it as it is in the first x axis order.</p>
  
  <p>So, <code>scale_x_discrete</code> ruins my plot. I tried factor and level editing also but they do not work either !</p>
  
  <p>Can anybody help to solve this issue? </p>
  
  <p>Thanks in advance.</p>