title: R ggplot too many labels
body: <p>I have this dataset:</p>
  
  <pre><code>x timw                y     class
  1 2010-04-01 00:00:00 843.2 normal
  2 2010-04-01 00:01:00 846.3 normal
  3 2010-04-01 00:02:00 838.6 normal
  4 2010-04-01 00:03:00 839.9 normal
  5 2010-04-01 00:04:00 841.0 normal
  6 2010-04-01 00:05:00 843.3 normal
  7 2010-04-01 00:06:00 844.2 normal
  8 2010-04-01 00:07:00 844.6 normal
  9 2010-04-01 00:08:00 840.0 normal
  10 2010-04-01 00:09:00 842.2 normal
  </code></pre>
  
  <p>I use ggplot in order to view data:</p>
  
  <pre><code>ggplot(df, aes(x=x, y=y)) + geom_point(aes(color=factor(class)))+
    scale_colour_manual(
      values = c("normal" = "green","early warning" = "orange","changepoint" = "red"))+
  theme(axis.text.x = element_text(face="bold", color="#993333", 
                                   size=14, angle=90)) +
    scale_x_discrete(limits=as.character(df$time))
  </code></pre>
  
  <p>The problem is that there is printed one timestamp foreach point, and if I increase the dataset size, the timestamps ovaelaps.</p>
  
  <p><img src="https://i.stack.imgur.com/sBfJQ.jpg" alt="100 timestamps picture"></p>
  
  <p>I tried to use <code>breaks</code> prameters in <code>scale_x_discrete</code> but it does not display any timestamp:</p>
  
  <pre><code>indexes&lt;-c(1,10,15)
  ggplot(df, aes(x=x, y=y)) + geom_point(aes(color=factor(class)))+
  scale_colour_manual(
  values = c("normal" = "green","early warning" = "orange","changepoint" = "red"))+
  theme(axis.text.x = element_text(face="bold", color="#993333", 
                               size=14, angle=90)) +
  scale_x_discrete(breaks=indexes limits=as.character(df$time))
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/m9PT2.jpg" alt="0 timestamps picture"></p>