title: Too many x-axis values on ggplot2 scatterplot
body: <p>I would be very thankful for anyone with advice on this. I think this is a <em>similar</em> to question to one previously posted here (<a href="https://stackoverflow.com/questions/15951216/too-many-factors-on-x-axis">Too many factors on x axis</a>).</p>
  
  <p>I  have a dataset as follows:</p>
  
  <pre><code>&gt; head(outputDF)
      var1    var2             snpR stepD
  1 A    B 1.55809163171629     6
  2 A    C 1.57475543745267     6
  3 A    D 1.36003481988361     4
  4 A    E 1.60338829251054     4
  5 A    F 1.54720598772132     5
  6 B    C 1.10321616677002     2 
  </code></pre>
  
  <p>I have a nice scatterplot from the function:</p>
  
  <pre><code>ggplot(outputDF, aes(x=snpR, y=stepD)) +geom_point(shape=1) +xlab("SNPR Distance") +
    ylab("StepD Distance")
  </code></pre>
  
  <p>But the problem is that since there are so many distinct snpR values on the x-axis, the x-axis numbers are unreadable, and there are too many vertical grids coming off each of these x-axis number labels.</p>
  
  <p>I know it is a trick with scale_x_continuous but I am just lost playing around with it...</p>