s='fl'>2</span>))</div><div class='output co'>#&gt; [1] 1 1 2 2</div><div class='input'><span class='fu'>library</span>(<span class='no'>dplyr</span>)
<span class='no'>df</span> <span class='kw'>&lt;-</span> <span class='fu'><a href='http://dplyr.tidyverse.org/reference/reexports.html'>data_frame</a></span>(<span class='kw'>id</span> <span class='kw'>=</span> <span class='fu'>c</span>(<span class='fl'>1</span>, <span class='fl'>1</span>, <span class='fl'>2</span>, <span class='fl'>2</span>), <span class='kw