title: R dplyr resolve variable in conditional filter
body: <p>I am trying to filter based on a variable value, and have tried multiple combinations of filter_, dots and quotes to no avail.</p>
  
  <p>As an example, I have a </p>
  
  <pre><code>runlist = c(1, 2, 3, 4, 5) 
  </code></pre>
  
  <p>and a dataframe boo</p>
  
  <pre><code>run &lt;- rep(seq(5), 3)
  edge1 &lt;- sample(20, 15)
  edge2 &lt;- sample(20, 15)
  weights &lt;- sample(50, 15)
  boo &lt;- as.data.frame(cbind(run, edge1, edge2, weights))
  </code></pre>
  
  <p>and I want to filter a dataframe named boo which may look something like
  iteratively as </p>
  
  <pre><code>for (i in runlist) {
      bop &lt;- boo %&gt;% filter( run == i )
      str(boo)
  }
  </code></pre>
  
  <p>I suspect I'll be hearing about not using for loops and R, rather use <code>group_by(run)</code>, but I'm sending this data to <code>igraph</code> and need to further subset the dataset to just edges and weights, thus losing the grouping variable, as in</p>
  
  <pre><code>bop &lt;- boo %&gt;% filter( run == i ) %&gt;% select( edge1, edge2, weights )
  </code></pre>
  
  <p>I will create a network graph and find density and centrality values for each run.</p>
  
  <pre><code>bing &lt;- graph.data.frame(bop)
  </code></pre>
  
  <p>How do I get the <code>i</code> in the conditional filter to resolve as the correct index?</p>