title: Remove duplicated rows using dplyr
body: <p>I have a data.frame like this - </p>
  
  <pre><code>set.seed(123)
  df = data.frame(x=sample(0:1,10,replace=T),y=sample(0:1,10,replace=T),z=1:10)
  &gt; df
     x y  z
  1  0 1  1
  2  1 0  2
  3  0 1  3
  4  1 1  4
  5  1 0  5
  6  0 1  6
  7  1 0  7
  8  1 0  8
  9  1 0  9
  10 0 1 10
  </code></pre>
  
  <p>I would like to remove duplicate rows based on first two columns. Expected output - </p>
  
  <pre><code>df[!duplicated(df[,1:2]),]
    x y z
  1 0 1 1
  2 1 0 2
  4 1 1 4
  </code></pre>
  
  <p>I am specifically looking for a solution using <code>dplyr</code> package.</p>