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Documentation for package ‘igraph’ version 0.7.1

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A B C D E F G H I K L M N O P Q R S T U V W misc

igraph-package The igraph package

-- A --

add.edges Method for structural manipulation of graphs
add.vertex.shape Various vertex shapes when plotting igraph graphs
add.vertices Method for structural manipulation of graphs
adjacent.triangles Count adjacenct triangles
aging.ba.game Generate an evolving random graph with preferential attachment and aging
aging.barabasi.game Generate an evolving random graph with preferential attachment and aging
aging.prefatt.game Generate an evolving random graph with preferential attachment and aging
algorithm Functions to deal with the result of network community detection
alpha.centrality Find Bonacich alpha centrality scores of network positions
are.connected Gaining information about graph structure
arpack ARPACK eigenvector calculation
arpack-options ARPACK eigenvector calculation
arpack.unpack.complex ARPACK eigenvector calculation
articulation.points Articulation points of a graph
as.dendrogram.communities Functions to deal with the result of network community detection
as.directed Convert between directed and undirected graphs
as.hclust.communities Functions to deal with the result of network community detection
as.igraph Conversion to igraph
as.igraph.igraphHRG Conversion to igraph
as.undirected Convert between directed and undirected graphs
asPhylo Functions to deal with the result of network community detection
asPhylo.communities Functions to deal with the result of network community detection
assortativity Assortativity coefficient
assortativity.degree Assortativity coefficient
assortativity.nominal Assortativity coefficient
asymmetric.preference.game Trait-based random generation
attribute.combination How igraph functions handle attributes when the graph changes
attributes Graph, vertex and edge attributes
authority.score Kleinberg's centrality scores.
autocurve.edges Optimal edge curvature when plotting graphs
average.path.length Shortest (directed or undirected) paths between vertices

-- B --

ba.game Generate scale-free graphs according to the Barabasi-Albert model
barabasi.game Generate scale-free graphs according to the Barabasi-Albert model
betweenness Vertex and edge betweenness centrality
betweenness.estimate Vertex and edge betweenness centrality
bibcoupling Cocitation coupling
biconnected.components Biconnected components
bipartite.mapping Decide whether a graph is bipartite
bipartite.projection Project a bipartite graph
bipartite.projection.size Project a bipartite graph
bipartite.random.game Bipartite random graphs
blockGraphs Calculate Cohesive Blocks
blocks Calculate Cohesive Blocks
bonpow Find Bonacich Power Centrality Scores of Network Positions

-- C --

callaway.traits.game Graph generation based on different vertex types
canonical.permutation Canonical permutation of a graph
centralization Centralization of a graph.tmax
centralization.betweenness Centralization of a graph.tmax
centralization.betweenness.tmax Centralization of a graph.tmax
centralization.closeness Centralization of a graph.tmax
centralization.closeness.tmax Centralization of a graph.tmax
centralization.degree Centralization of a graph.tmax
centralization.degree.tmax Centralization of a graph.tmax
centralization.evcent Centralization of a graph.tmax
centralization.evcent.tmax Centralization of a graph.tmax
centralize.scores Centralization of a graph.tmax
cited.type.game Undocumented and unsupportted igraph functions
citing.cited.type.game Undocumented and unsupportted igraph functions
clique.number The functions find cliques, ie. complete subgraphs in a graph
cliques The functions find cliques, ie. complete subgraphs in a graph
closeness Closeness centrality of vertices
closeness.estimate Closeness centrality of vertices
cluster.distribution Connected components of a graph
clusters Connected components of a graph
cocitation Cocitation coupling
code.length Functions to deal with the result of network community detection
cohesion Calculate Cohesive Blocks
cohesive.blocks Calculate Cohesive Blocks
cohesiveBlocks Calculate Cohesive Blocks
communities Functions to deal with the result of network community detection
community.le.to.membership Community structure detecting based on the leading eigenvector of the community matrix
community.to.membership Common functions supporting community detection algorithms
compare Compares community structures using various metrics
compare.communities Compares community structures using various metrics
compare.numeric Compares community structures using various metrics
connect.neighborhood Neighborhood of graph vertices
constraint Burt's constraint
contract.vertices Contract several vertices into a single one
convex.hull Convex hull of a set of vertices
count.multiple Find the multiple or loop edges in a graph
create.communities Functions to deal with the result of network community detection
crossing Functions to deal with the result of network community detection
cutat Functions to deal with the result of network community detection

-- D --

decompose.graph Decompose a graph into components
degree Degree and degree distribution of the vertices
degree.distribution Degree and degree distribution of the vertices
degree.sequence.game Generate random graphs with a given degree sequence
delete.edges Method for structural manipulation of graphs
delete.vertices Method for structural manipulation of graphs
dendPlot Plot dendrograms
dendPlot.communities Community structure dendrogram plots
dendPlot.igraphHRG HRG dendrogram plot
diameter Diameter of a graph
DL Reading foreign file formats
dominator.tree Dominator tree
dyad.census Dyad census of a graph

-- E --

E Vertex and edge sequences and iterators
E<- Vertex and edge sequences and iterators
eccentricity Eccentricity and radius
ecount Gaining information about graph structure
edge Method for structural manipulation of graphs
edge.attributes Graph, vertex and edge attributes
edge.attributes<- Graph, vertex and edge attributes
edge.betweenness Vertex and edge betweenness centrality
edge.betweenness.community Community structure detection based on edge betweenness
edge.betweenness.community.merges Community structure detection based on edge betweenness
edge.betweenness.estimate Vertex and edge betweenness centrality
edge.connectivity Edge connectivity.
edge.disjoint.paths Edge connectivity.
edges Method for structural manipulation of graphs
erdos.renyi.game Generate random graphs according to the Erdos-Renyi model
establishment.game Graph generation based on different vertex types
evcent Find Eigenvector Centrality Scores of Network Positions
evolver Measuring the driving force in evolving networks
evolver.d Measuring the driving force in evolving networks
exportPajek Calculate Cohesive Blocks

-- F --

farthest.nodes Diameter of a graph
fastgreedy.community Community structure via greedy optimization of modularity
forest.fire.game Forest Fire Network Model

-- G --

get.adjacency Convert a graph to an adjacency matrix or an edge list
get.adjedgelist Adjacency lists
get.adjlist Adjacency lists
get.all.shortest.paths Shortest (directed or undirected) paths between vertices
get.data.frame Creating igraph graphs from data frames or vice-versa
get.diameter Diameter of a graph
get.edge Gaining information about graph structure
get.edge.attribute Graph, vertex and edge attributes
get.edge.ids Find the edge ids based on the incident vertices of the edges
get.edgelist Convert a graph to an adjacency matrix or an edge list
get.edges Gaining information about graph structure
get.graph.attribute Graph, vertex and edge attributes
get.incidence Incidence matrix of a bipartite graph
get.shortest.paths Shortest (directed or undirected) paths between vertices
get.stochastic Stochastic matrix of a graph
get.vertex.attribute Graph, vertex and edge attributes
getIgraphOpt Parameters for the igraph package
girth Girth of a graph
GML Reading foreign file formats
graph Various methods for creating graphs
graph.adhesion Edge connectivity.
graph.adjacency Create graphs from adjacency matrices
graph.adjlist Create graphs from adjacency lists
graph.atlas Various methods for creating graphs
graph.attributes Graph, vertex and edge attributes
graph.attributes<- Graph, vertex and edge attributes
graph.automorphisms Number of automorphisms
graph.bfs Breadth-first search
graph.bipartite Create a bipartite graph
graph.cohesion Vertex connectivity.
graph.complementer Complementer of a graph
graph.compose Compose two graphs as binary relations
graph.constructors Various methods for creating graphs
graph.coreness K-core decomposition of graphs
graph.count.isomorphisms.vf2 Graph Isomorphism
graph.count.subisomorphisms.vf2 Graph Isomorphism
graph.data.frame Creating igraph graphs from data frames or vice-versa
graph.de.bruijn De Bruijn graphs.
graph.density Graph density
graph.dfs Depth-first search
graph.difference Difference of graphs
graph.disjoint.union Disjoint union of graphs
graph.diversity Graph diversity
graph.edgelist Various methods for creating graphs
graph.eigen Eigenvalues and eigenvectors of the adjacency matrix of a graph
graph.empty Various methods for creating graphs
graph.extended.chordal.ring Various methods for creating graphs
graph.famous Creating named graphs
graph.formula Creating (small) graphs via a simple interface
graph.full Various methods for creating graphs
graph.full.bipartite Create a full bipartite graph
graph.full.citation Various methods for creating graphs
graph.get.isomorphisms.vf2 Graph Isomorphism
graph.get.subisomorphisms.vf2 Graph Isomorphism
graph.graphdb Load a graph from the graph database for testing graph isomorphism.
graph.incidence Create graphs from an incidence matrix
graph.intersection Intersection of graphs
graph.isoclass Graph Isomorphism
graph.isoclass.subgraph Graph Isomorphism
graph.isocreate Graph Isomorphism
graph.isomorphic Graph Isomorphism
graph.isomorphic.34 Graph Isomorphism
graph.isomorphic.bliss Graph Isomorphism
graph.isomorphic.vf2 Graph Isomorphism
graph.kautz Kautz graphs
graph.knn Average nearest neighbor degree
graph.laplacian Graph Laplacian
graph.lattice Various methods for creating graphs
graph.lcf Creating a graph from LCF notation
graph.maxflow Maximum flow in a network
graph.mincut Maximum flow in a network
graph.motifs Graph motifs
graph.motifs.est Graph motifs
graph.motifs.no Graph motifs
graph.neighborhood Neighborhood of graph vertices
graph.ring Various methods for creating graphs
graph.star Various methods for creating graphs
graph.strength Strength or weighted vertex degree
graph.subisomorphic.lad Graph Isomorphism
graph.subisomorphic.vf2 Graph Isomorphism
graph.tree Various methods for creating graphs
graph.union Union of graphs
graphlets Graphlet decomposition of a graph
graphlets.candidate.basis Graphlet decomposition of a graph
graphlets.project Graphlet decomposition of a graph
GraphML Reading foreign file formats
grg.game Geometric random graphs
growing.random.game Growing random graph generation

-- H --

has.multiple Find the multiple or loop edges in a graph
hierarchy Calculate Cohesive Blocks
HRG Hierarchical random graphs
hrg.consensus Hierarchical random graphs
hrg.create Hierarchical random graphs
hrg.dendrogram Hierarchical random graphs
hrg.fit Hierarchical random graphs
hrg.game Hierarchical random graphs
hrg.predict Hierarchical random graphs
hub.score Kleinberg's centrality scores.

-- I --

igraph The igraph package
igraph.arpack.default ARPACK eigenvector calculation
igraph.console The igraph console
igraph.drl.coarsen The DrL graph layout generator
igraph.drl.coarsest The DrL graph layout generator
igraph.drl.default The DrL graph layout generator
igraph.drl.final The DrL graph layout generator
igraph.drl.refine The DrL graph layout generator
igraph.eigen.default Eigenvalues and eigenvectors of the adjacency matrix of a graph
igraph.from.graphNEL Convert igraph graphs to graphNEL objects or back
igraph.options Parameters for the igraph package
igraph.par Parameters for the igraph package
igraph.plotting Drawing graphs
igraph.sample Sampling a random integer sequence
igraph.shape.noclip Various vertex shapes when plotting igraph graphs
igraph.shape.noplot Various vertex shapes when plotting igraph graphs
igraph.to.graphNEL Convert igraph graphs to graphNEL objects or back
igraph.version Query igraph's version string
igraph.vertex.shapes Various vertex shapes when plotting igraph graphs
igraphdemo Run igraph demos, step by step
igraphtest Run package tests
incident Gaining information about graph structure
independence.number Independent vertex sets
independent.vertex.sets Independent vertex sets
induced.subgraph Subgraph of a graph
infomap.community Infomap community finding
interconnected.islands.game A graph with subgraphs that are each a random graph.
is.bipartite Create a bipartite graph
is.chordal Chordality of a graph
is.connected Connected components of a graph
is.dag Directed acyclic graphs
is.degree.sequence Degree sequences of graphs
is.directed Gaining information about graph structure
is.graphical.degree.sequence Degree sequences of graphs
is.hierarchical Functions to deal with the result of network community detection
is.igraph Is this object a graph?
is.loop Find the multiple or loop edges in a graph
is.matching Graph matching
is.maximal.matching Graph matching
is.minimal.separator Vertex separators
is.multiple Find the multiple or loop edges in a graph
is.mutual Find mutual edges in a directed graph
is.named Named graphs
is.separator Vertex separators
is.simple Simple graphs
is.weighted Weighted graphs
iterators Vertex and edge sequences and iterators

-- K --

k.regular.game Create a random regular graph

-- L --

label.propagation.community Finding communities based on propagating labels
largest.cliques The functions find cliques, ie. complete subgraphs in a graph
largest.independent.vertex.sets Independent vertex sets
lastcit.game Undocumented and unsupportted igraph functions
layout Generate coordinates for plotting graphs
layout.auto Generate coordinates for plotting graphs
layout.bipartite Simple two-row layout for bipartite graphs
layout.circle Generate coordinates for plotting graphs
layout.drl The DrL graph layout generator
layout.fruchterman.reingold Generate coordinates for plotting graphs
layout.fruchterman.reingold.grid Generate coordinates for plotting graphs
layout.graphopt Generate coordinates for plotting graphs
layout.grid Simple grid layout
layout.grid.3d Simple grid layout
layout.kamada.kawai Generate coordinates for plotting graphs
layout.lgl Generate coordinates for plotting graphs
layout.mds Graph layout by multidimensional scaling
layout.merge Merging graph layouts
layout.norm Generate coordinates for plotting graphs
layout.random Generate coordinates for plotting graphs
layout.reingold.tilford Generate coordinates for plotting graphs
layout.sphere Generate coordinates for plotting graphs
layout.spring Generate coordinates for plotting graphs
layout.star Generate coordinates to place the vertices of a graph in a star-shape
layout.sugiyama The Sugiyama graph layout generator
layout.svd Generate coordinates for plotting graphs
leading.eigenvector.community Community structure detecting based on the leading eigenvector of the community matrix
length.cohesiveBlocks Calculate Cohesive Blocks
length.communities Functions to deal with the result of network community detection
LGL Reading foreign file formats
line.graph Line graph of a graph
list.edge.attributes Graph, vertex and edge attributes
list.graph.attributes Graph, vertex and edge attributes
list.vertex.attributes Graph, vertex and edge attributes

-- M --

maxcohesion Calculate Cohesive Blocks
maximal.cliques The functions find cliques, ie. complete subgraphs in a graph
maximal.cliques.count The functions find cliques, ie. complete subgraphs in a graph
maximal.independent.vertex.sets Independent vertex sets
maximum.bipartite.matching Graph matching
maximum.cardinality.search Maximum cardinality search
median.sir SIR model on graphs
membership Functions to deal with the result of network community detection
merges Functions to deal with the result of network community detection
minimal.st.separators Minimum size vertex separators
minimum.size.separators Minimum size vertex separators
minimum.spanning.tree Minimum spanning tree
mod.matrix Modularity of a community structure of a graph
modularity Modularity of a community structure of a graph
modularity.communities Functions to deal with the result of network community detection
modularity.igraph Modularity of a community structure of a graph
multilevel.community Finding community structure by multi-level optimization of modularity

-- N --

neighborhood Neighborhood of graph vertices
neighborhood.size Neighborhood of graph vertices
neighbors Gaining information about graph structure
nexus Query and download from the Nexus network repository
nexus.get Query and download from the Nexus network repository
nexus.info Query and download from the Nexus network repository
nexus.list Query and download from the Nexus network repository
nexus.search Query and download from the Nexus network repository
nexusDatasetInfo Query and download from the Nexus network repository
no.clusters Connected components of a graph

-- O --

optimal.community Optimal community structure

-- P --

page.rank The Page Rank algorithm
page.rank.old The Page Rank algorithm
Pajek Reading foreign file formats
parent Calculate Cohesive Blocks
path Method for structural manipulation of graphs
path.length.hist Shortest (directed or undirected) paths between vertices
permute.vertices Permute the vertices of a graph
piecewise.layout Merging graph layouts
plot.cohesiveBlocks Calculate Cohesive Blocks
plot.communities Functions to deal with the result of network community detection
plot.igraph Plotting of graphs
plot.sir Plotting the results on multiple SIR model runs
plotHierarchy Calculate Cohesive Blocks
power.law.fit Fitting a power-law distribution function to discrete data
preference.game Trait-based random generation
print.cohesiveBlocks Calculate Cohesive Blocks
print.communities Functions to deal with the result of network community detection
print.igraph Print graphs to the terminal
print.igraph.es Vertex and edge sequences and iterators
print.igraph.vs Vertex and edge sequences and iterators
print.igraphHRG Hierarchical random graphs
print.igraphHRGConsensus Hierarchical random graphs
print.nexusDatasetInfo Query and download from the Nexus network repository
print.nexusDatasetInfoList Query and download from the Nexus network repository

-- Q --

quantile.sir SIR model on graphs

-- R --

radius Eccentricity and radius
random.graph.game Generate random graphs according to the Erdos-Renyi model
read.graph Reading foreign file formats
reciprocity Reciprocity of graphs
remove.edge.attribute Graph, vertex and edge attributes
remove.graph.attribute Graph, vertex and edge attributes
remove.vertex.attribute Graph, vertex and edge attributes
revolver Measuring the driving force in evolving networks
revolver.ad Measuring the driving force in evolving networks
revolver.ade Measuring the driving force in evolving networks
revolver.adi Measuring the driving force in evolving networks
revolver.air Measuring the driving force in evolving networks
revolver.ar Measuring the driving force in evolving networks
revolver.d Measuring the driving force in evolving networks
revolver.d.d Measuring the driving force in evolving networks
revolver.de Measuring the driving force in evolving networks
revolver.di Measuring the driving force in evolving networks
revolver.dl Measuring the driving force in evolving networks
revolver.e Measuring the driving force in evolving networks
revolver.el Measuring the driving force in evolving networks
revolver.error.ad Measuring the driving force in evolving networks
revolver.error.ade Measuring the driving force in evolving networks
revolver.error.adi Measuring the driving force in evolving networks
revolver.error.air Measuring the driving force in evolving networks
revolver.error.ar Measuring the driving force in evolving networks
revolver.error.d Measuring the driving force in evolving networks
revolver.error.de Measuring the driving force in evolving networks
revolver.error.di Measuring the driving force in evolving networks
revolver.error.dl Measuring the driving force in evolving networks
revolver.error.e Measuring the driving force in evolving networks
revolver.error.el Measuring the driving force in evolving networks
revolver.error.il Measuring the driving force in evolving networks
revolver.error.ir Measuring the driving force in evolving networks
revolver.error.l Measuring the driving force in evolving networks
revolver.error.r Measuring the driving force in evolving networks
revolver.il Measuring the driving force in evolving networks
revolver.ir Measuring the driving force in evolving networks
revolver.l Measuring the driving force in evolving networks
revolver.ml.ad Measuring the driving force in evolving networks
revolver.ml.AD.alpha.a.beta Measuring the driving force in evolving networks
revolver.ml.AD.dpareto Measuring the driving force in evolving networks
revolver.ml.AD.dpareto.eval Measuring the driving force in evolving networks
revolver.ml.ade Measuring the driving force in evolving networks
revolver.ml.ADE.alpha.a.beta Measuring the driving force in evolving networks
revolver.ml.ADE.dpareto Measuring the driving force in evolving networks
revolver.ml.ADE.dpareto.eval Measuring the driving force in evolving networks
revolver.ml.ADE.dpareto.evalf Measuring the driving force in evolving networks
revolver.ml.d Measuring the driving force in evolving networks
revolver.ml.D.alpha Measuring the driving force in evolving networks
revolver.ml.D.alpha.a Measuring the driving force in evolving networks
revolver.ml.de Measuring the driving force in evolving networks
revolver.ml.DE.alpha.a Measuring the driving force in evolving networks
revolver.ml.df Measuring the driving force in evolving networks
revolver.ml.f Measuring the driving force in evolving networks
revolver.ml.l Measuring the driving force in evolving networks
revolver.p.p Measuring the driving force in evolving networks
revolver.probs.ad Measuring the driving force in evolving networks
revolver.probs.ade Measuring the driving force in evolving networks
revolver.probs.ADE.dpareto Measuring the driving force in evolving networks
revolver.probs.d Measuring the driving force in evolving networks
revolver.probs.de Measuring the driving force in evolving networks
revolver.r Measuring the driving force in evolving networks
rewire Graph rewiring
rewire.edges Rewires the endpoints of the edges of a graph randomly
rglplot 3D plotting of graphs with OpenGL
rglplot.igraph 3D plotting of graphs with OpenGL
running.mean Running mean of a time series

-- S --

sbm.game Sample stochastic block model
SCG Spectral Coarse Graining
scg All-in-one Function for the SCG of Matrices and Graphs
scgGrouping SCG Problem Solver
scgNormEps SCG Extra Functions
scgSemiProjectors Semi-Projectors
set.edge.attribute Graph, vertex and edge attributes
set.graph.attribute Graph, vertex and edge attributes
set.vertex.attribute Graph, vertex and edge attributes
shortest.paths Shortest (directed or undirected) paths between vertices
showtrace Functions to deal with the result of network community detection
similarity.dice Similarity measures of two vertices
similarity.invlogweighted Similarity measures of two vertices
similarity.jaccard Similarity measures of two vertices
simplify Simple graphs
sir SIR model on graphs
sizes Functions to deal with the result of network community detection
spinglass.community Finding communities in graphs based on statistical meachanics
srand Set random seed of the C library's RNG
static.fitness.game Random graphs from vertex fitness scores
static.power.law.game Scale-free random graphs, from vertex fitness scores
stCuts List all (s,t)-cuts of a graph
stMincuts List all minimum (s,t)-cuts of a graph
str.igraph Print graphs to the terminal
subcomponent In- or out- component of a vertex
subgraph Subgraph of a graph
subgraph.centrality Find subgraph centrality scores of network positions
subgraph.edges Subgraph of a graph
summary.cohesiveBlocks Calculate Cohesive Blocks
summary.igraph Print graphs to the terminal
summary.nexusDatasetInfoList Query and download from the Nexus network repository

-- T --

time_bins SIR model on graphs
time_bins.sir SIR model on graphs
tkigraph Experimental basic igraph GUI
tkplot Interactive plotting of graphs
tkplot.canvas Interactive plotting of graphs
tkplot.center Interactive plotting of graphs
tkplot.close Interactive plotting of graphs
tkplot.export.postscript Interactive plotting of graphs
tkplot.fit.to.screen Interactive plotting of graphs
tkplot.getcoords Interactive plotting of graphs
tkplot.off Interactive plotting of graphs
tkplot.reshape Interactive plotting of graphs
tkplot.rotate Interactive plotting of graphs
tkplot.setcoords Interactive plotting of graphs
topological.sort Topological sorting of vertices in a graph
transitivity Transitivity of a graph
triad.census Triad census, subgraphs with three vertices

-- U --

UCINET Reading foreign file formats
unfold.tree Convert a general graph into a forest

-- V --

V Vertex and edge sequences and iterators
V<- Vertex and edge sequences and iterators
vcount Gaining information about graph structure
vertex Method for structural manipulation of graphs
vertex.attributes Graph, vertex and edge attributes
vertex.attributes<- Graph, vertex and edge attributes
vertex.connectivity Vertex connectivity.
vertex.disjoint.paths Vertex connectivity.
vertex.shape.pie Using pie charts as vertices in graph plots
vertex.shapes Various vertex shapes when plotting igraph graphs
vertices Method for structural manipulation of graphs

-- W --

walktrap.community Community strucure via short random walks
watts.strogatz.game The Watts-Strogatz small-world model
write.graph Writing the graph to a file in some format

-- misc --

$.igraph.es Vertex and edge sequences and iterators
$.igraph.vs Vertex and edge sequences and iterators
$<-.igraph.es Vertex and edge sequences and iterators
$<-.igraph.vs Vertex and edge sequences and iterators
%--% Vertex and edge sequences and iterators
%->% Vertex and edge sequences and iterators
%<-% Vertex and edge sequences and iterators
%c% Compose two graphs as binary relations
%du% Disjoint union of graphs
%m% Difference of graphs
%s% Intersection of graphs
%u% Union of graphs
+.igraph Method for structural manipulation of graphs
-.igraph Method for structural manipulation of graphs
[.igraph Method for structural manipulation of graphs
[.igraph.es Vertex and edge sequences and iterators
[.igraph.vs Vertex and edge sequences and iterators
[<-.igraph Method for structural manipulation of graphs
[<-.igraph.es Vertex and edge sequences and iterators
[<-.igraph.vs Vertex and edge sequences and iterators
[[.igraph Method for structural manipulation of graphs
[[.igraph.es Vertex and edge sequences and iterators
[[.igraph.vs Vertex and edge sequences and iterators
[[<-.igraph.es Vertex and edge sequences and iterators
[[<-.igraph.vs Vertex and edge sequences and iterators