[igraph] (R) Error plotting a graph over two layers

[Francesco]

Hello everyone
I get the following error

Error in mapply(loop, xx0, yy0, color = ec, angle = -la, label = loop.labels,  
: 
  zero-length inputs cannot be mixed with those of non-zero length
In addition: Warning message:
In max(vertex.size) : no non-missing arguments to max; returning -Inf

when plotting a graph over two layers with

par(mar=c(0,0,0,0))
layout <- layout.circle(igraph_thread_parentCategories)
plot(igraph_thread_parentCategories,
     layout=layout,
     vertex.label=NA,
     vertex.frame.color=NA,
     edge.width=(E(igraph_thread_parentCategories)$weight)/300000,
     vertex.size=log(V(igraph_thread_parentCategories)$category_size)*2)
plot(igraph_thread_parentCategories,
     add=TRUE,
     layout=layout,
     vertex.label.color="black",
     edge.label.color="black",
     vertex.label.family="Palatino",
     edge.label.family="Palatino",
     edge.label.cex=0.6,
     edge.loop.angle=0.1,
     edge.label=sub("[ ]+", "", 
format(E(igraph_thread_parentCategories)$weight, big.mark=",", 
scientific=FALSE)),
     edge.width=0.001,
     vertex.label.cex=log(V(igraph_thread_parentCategories)$category_size)/8,
     vertex.shape="none",
     vertex.label=V(igraph_thread_parentCategories)$parentCategory)

Nevertheless if I try to write the graph in graphml and then import it again in 
R I don’t get the error anymore and I plot without problems…

I attach the graph in graphml below:

<?xml version="1.0" encoding="UTF-8"?>
<graphml xmlns="http://graphml.graphdrawing.org/xmlns";
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance";
         xsi:schemaLocation="http://graphml.graphdrawing.org/xmlns
         http://graphml.graphdrawing.org/xmlns/1.0/graphml.xsd";>
<!-- Created by igraph -->
  <key id="v_category_size" for="node" attr.name="category_size" 
attr.type="double"/>
  <key id="v_parentCategory" for="node" attr.name="parentCategory" 
attr.type="string"/>
  <key id="e_weight" for="edge" attr.name="weight" attr.type="double"/>
  <graph id="G" edgedefault="undirected">
    <node id="n0">
      <data key="v_category_size">1</data>
      <data key="v_parentCategory">Acqua</data>
    </node>
    <node id="n1">
      <data key="v_category_size">26266</data>
      <data key="v_parentCategory">Development</data>
    </node>
    <node id="n2">
      <data key="v_category_size">3319</data>
      <data key="v_parentCategory">Energy</data>
    </node>
    <node id="n3">
      <data key="v_category_size">2106</data>
      <data key="v_parentCategory">Environment</data>
    </node>
    <node id="n4">
      <data key="v_category_size">27835</data>
      <data key="v_parentCategory">Forum</data>
    </node>
    <node id="n5">
      <data key="v_category_size">748</data>
      <data key="v_parentCategory">No label</data>
    </node>
    <node id="n6">
      <data key="v_category_size">20450</data>
      <data key="v_parentCategory">Services</data>
    </node>
    <node id="n7">
      <data key="v_category_size">2958</data>
      <data key="v_parentCategory">Transport</data>
    </node>
    <node id="n8">
      <data key="v_category_size">3260</data>
      <data key="v_parentCategory">Water</data>
    </node>
    <edge source="n1" target="n1">
      <data key="e_weight">6.95214e+06</data>
    </edge>
    <edge source="n1" target="n2">
      <data key="e_weight">1.51071e+06</data>
    </edge>
    <edge source="n1" target="n3">
      <data key="e_weight">956584</data>
    </edge>
    <edge source="n1" target="n4">
      <data key="e_weight">1.53941e+07</data>
    </edge>
    <edge source="n1" target="n5">
      <data key="e_weight">73424</data>
    </edge>
    <edge source="n1" target="n6">
      <data key="e_weight">1.20328e+07</data>
    </edge>
    <edge source="n1" target="n7">
      <data key="e_weight">1.13116e+06</data>
    </edge>
    <edge source="n1" target="n8">
      <data key="e_weight">1.82569e+06</data>
    </edge>
    <edge source="n2" target="n2">
      <data key="e_weight">114710</data>
    </edge>
    <edge source="n2" target="n3">
      <data key="e_weight">103203</data>
    </edge>
    <edge source="n2" target="n4">
      <data key="e_weight">1.78563e+06</data>
    </edge>
    <edge source="n2" target="n5">
      <data key="e_weight">12189</data>
    </edge>
    <edge source="n2" target="n6">
      <data key="e_weight">1.37112e+06</data>
    </edge>
    <edge source="n2" target="n7">
      <data key="e_weight">121806</data>
    </edge>
    <edge source="n2" target="n8">
      <data key="e_weight">213611</data>
    </edge>
    <edge source="n3" target="n3">
      <data key="e_weight">37994</data>
    </edge>
    <edge source="n3" target="n4">
      <data key="e_weight">1.0159e+06</data>
    </edge>
    <edge source="n3" target="n5">
      <data key="e_weight">4404</data>
    </edge>
    <edge source="n3" target="n6">
      <data key="e_weight">795618</data>
    </edge>
    <edge source="n3" target="n7">
      <data key="e_weight">81201</data>
    </edge>
    <edge source="n3" target="n8">
      <data key="e_weight">121390</data>
    </edge>
    <edge source="n4" target="n4">
      <data key="e_weight">1.03954e+07</data>
    </edge>
    <edge source="n4" target="n5">
      <data key="e_weight">87206</data>
    </edge>
    <edge source="n4" target="n6">
      <data key="e_weight">1.5082e+07</data>
    </edge>
    <edge source="n4" target="n7">
      <data key="e_weight">1.24879e+06</data>
    </edge>
    <edge source="n4" target="n8">
      <data key="e_weight">2.17e+06</data>
    </edge>
    <edge source="n5" target="n5">
      <data key="e_weight">7681</data>
    </edge>
    <edge source="n5" target="n6">
      <data key="e_weight">74487</data>
    </edge>
    <edge source="n5" target="n7">
      <data key="e_weight">6167</data>
    </edge>
    <edge source="n5" target="n8">
      <data key="e_weight">8575</data>
    </edge>
    <edge source="n6" target="n6">
      <data key="e_weight">6.34569e+06</data>
    </edge>
    <edge source="n6" target="n7">
      <data key="e_weight">984899</data>
    </edge>
    <edge source="n6" target="n8">
      <data key="e_weight">1.69744e+06</data>
    </edge>
    <edge source="n7" target="n7">
      <data key="e_weight">53031</data>
    </edge>
    <edge source="n7" target="n8">
      <data key="e_weight">147161</data>
    </edge>
    <edge source="n8" target="n8">
      <data key="e_weight">159503</data>
    </edge>
  </graph>
</graphml>