title: What is the difference between `%in%` and `==`?
body: <pre><code>df &lt;- structure(list(x = 1:10, time = c(0.5, 0.5, 1, 2, 3, 0.5, 0.5, 
  1, 2, 3)), .Names = c("x", "time"), row.names = c(NA, -10L), class = "data.frame")
  
  
  df[df$time %in% c(0.5, 3), ]
  ##     x time
  ## 1   1  0.5
  ## 2   2  0.5
  ## 5   5  3.0
  ## 6   6  0.5
  ## 7   7  0.5
  ## 10 10  3.0
  
  df[df$time == c(0.5, 3), ]
  ##     x time
  ## 1   1  0.5
  ## 7   7  0.5
  ## 10 10  3.0
  </code></pre>
  
  <p>What is the difference between <code>%in%</code> and <code>==</code> here? </p>