title: ggplot x-axis labels with all x-axis values
body: <p>I'm plotting <code>ggplot</code> with <code>geom_point</code>. The x-axis will be individuals' ID, and y-axis is variable A. How can I ggplot all and individual ID values on the x-axis without overlapping labels? ID may not be continuous.</p>
  
  <p>df sample (actual rows are much longer)</p>
  
  <pre><code>&gt; df
  ID     A
  1      4
  2      12
  3      45
  5      1
  </code></pre>
  
  <p>Code for the plot:</p>
  
  <pre><code>ggplot(df, aes(x = ID, y = A)) + geom_point()
  </code></pre>
  
  <p>Above code has x-axis in intervals, but not presenting individual ID.</p>
  
  <p>Thanks!</p>