title: R ggraph remove isolates when facet_edges specified
body: <p>I am doing some exploratory network analysis with the <code>tidygraph</code> package. I am trying to produce a faceted plot with my data using <code>ggraph</code> package. I created 2 different <code>tbl_graph</code> objects, which I bound together using the <code>bind_graphs</code> function.</p>
  <p>The code I am using is:</p>
  <pre class="lang-r prettyprint-override"><code># 1) Creating full graph
  g.tot.1 &lt;- tbl_graph(nodes = nodes, edges = fdi) %&gt;%
    activate(edges) %&gt;% filter(sector == 'Financial services') %&gt;%
    activate(nodes) %&gt;% filter(!node_is_isolated()) %&gt;%
    activate(edges) %&gt;% mutate(tofrom = ifelse(.N()$name[to] == 'DUB', 1, 2)) 
  
  # 2) creating &quot;to DUB&quot; graph 
  g.to.1 &lt;- g.tot.1 %&gt;%
    filter(tofrom == 1) %&gt;%
    activate(nodes) %&gt;% filter(!node_is_isolated()) %&gt;%
    
  # 3) Creating &quot;from DUB&quot; graph
  g.from.1 &lt;- g.tot.1 %&gt;%
    filter(tofrom == 2) %&gt;%
    activate(nodes) %&gt;% filter(!node_is_isolated()) %&gt;%
  
  # Binding graphs and plotting the result
  ggraph(bind_graphs(g.to.1, g.from.1), layout = 'fr') %&gt;%
    facet_edges(~tofrom) + 
    geom_edge_link(arrow = arrow()) +
    #geom_node_point(size = 5, colour = 'steelblue') +
    #geom_node_text(aes(label = iso), colour = 'black', vjust = 0.4) +
    ggtitle('FDI From and To Dubai') +
    theme_graph(foreground = 'steelblue')
  </code></pre>
  <p>Despite a large number of warnings, I still obtain a faceted graph. However, the faceted graphs still plot all the isolates, despite the <code>filter(!node_is_isolated())</code> call in both the subgraphs. This does not happen when I avoid specifying the <code>facet_edges</code> option.</p>
  <p>Any help would be greatly appreciated.</p>