R Programming/Network Analysis

R Programming/analysis

Introduction

We mainly use the following packages to demonstrate network analysis in R: statnet, sna, igraph. They are however not representing a complete list. See Task view of gR, graphical models in R for a complete list.

Creating simple graphs with igraph

 
> # load the appropriate library
> library(igraph)
> # now create a few simple graphs
> # an undirected graph with 10 nodes and without any edge
> g1 <- graph.empty(10,directed=FALSE)
> # a directed graph with 10 nodes
> g2 <- graph.ring(10,directed=TRUE)
> # a complete undirected graph with 10 nodes
> g3 <- graph.full(10,directed=FALSE)
> # now get information about these graphs
> summary(g1)
> # g1 is an igraph object, U = Undirected, with 10 nodes and 0 edge
> IGRAPH U--- 10 0 -- 
> summary(g2)
> # g1 is an igraph object,  D = Directed
> IGRAPH D--- 10 10 -- Ring graph

Creating graphs from data

First load the igraph package

library(igraph)

then you can choose your preferred format. Below are examples of data provided as edge list and as adjacency matrix.

Creating graph from an edge list

An edge list is formed by a two-column matrix, with each row defining one edge. An edge is drawn from each element in the first column to the corresponding element in the second one. Use the graph.edgelist() function to import your data.

 
# producing some random data in edge list form
el <- cbind(sample(1:10, 10), sample(1:10, 10))

# creating and plotting the graph from the edge list
gr <- graph.edgelist(el)
plot(gr)

Creating graph from an adjacency matrix

An adjacency matrix is a n × n matrix containing n vertices and where each entry a_ij represents the number of edges from vertex i to vertex j. To import your adjacency matrix, use the graph.adjacency() function.

 
# producing a random adjacency matrix
adj <- matrix(sample(0:1, 100, replace=T), 10, 10)

# creating and plottig the graph from the adjacency matrix
gr <- graph.adjacency(adj)
plot(gr)

References

• Statnet website includes all the documentation on network analysis using R.
• Julien Barnier's introduction (in French)
• Journal of Statistical Software #24 Special Issue on Networks in R