title: Remove same columns from left_join
body: <p>I'd like to merge two data frames by <code>id</code>, but they both have 2 of the same columns; therefore, when I merge i get new <code>.x</code> and <code>.y</code> columns.  How can I merge these two data frames with <code>left_join()</code> and remove the extra columns currently in my code that are the same (`element.x, day.x, element.y, and day.y) and keep a single column.</p>
  
  <p>Code:</p>
  
  <pre><code># Sample data
  df1 &lt;- data.frame(id = seq(1,5), value1 = rnorm(5), element = "TEST1", day = 15) 
  df2 &lt;- data.frame(id = seq(1,5), value2 = rnorm(5), element = "TEST1", day = 15) 
  
  # Merge
  df &lt;- left_join(df1, df2, by = "id")
  
  # Output
    id      value1 element.x day.x     value2 element.y day.y
  1  1 -0.69700149     TEST1    15  1.4324220     TEST1    15
  2  2 -0.25514949     TEST1    15  0.7281354     TEST1    15
  3  3  0.09206902     TEST1    15  0.8148839     TEST1    15
  4  4  2.51799237     TEST1    15  1.3919671     TEST1    15
  5  5 -0.77049050     TEST1    15 -0.2707201     TEST1    15
  </code></pre>