Starting from the Adjacency Matrix with igraph

To avoid mistakes and confusion, it is better to detach the statnet package because there exist similar functions to the ones of the igraph package. If we do not detach the statnet package, we have to use the prefix network:: to specify that the function is from the network package (which is included in the statnet package).

detach(package:statnet)
p_load(igraph)

Now, the starting point is the adjacency matrix again. This is equal to what has been done before.

adjacency_matrix <- rbind(
  c(0,1,1,0,0),
  c(0,0,1,1,0),
  c(0,1,0,0,0),
  c(0,0,0,0,0),
  c(0,0,1,0,0)
)

Creating a Network Object

Now that we have our matrix, we can create a network object from it using the graph.adjacency() function from the igraph package:

adjacency_network <- graph.adjacency(adjacency_matrix)

Checking the Network Object

To confirm that our network object was created successfully, we can check its class type with the class() function:

class(adjacency_network)

[1] "igraph"

We can also use the summary() function to get more information about the network, such as the number of vertices and edges:

summary(adjacency_network)

IGRAPH 50042ad DN-- 5 6 --
+ attr: name (v/c)

Understanding the Summary Output

• IGRAPH : The first line always starts with IGRAPH, showing that the object is an igraph graph.

• 50042ad : A seven character code is printed. The code stands for the unique id of the graph but is not important to remember.

• DN-- : A four letter long code string is printed.
  • The first letter distinguishes between directed (“D”) and undirected (“U”) graphs.
  • The second letter is “N” for named graphs, i.e. graphs with the name vertex attribute set.
  • The third letter is “W” for weighted graphs, i.e. graphs with the weight edge attribute set.
  • The fourth letter is “B” for bipartite graphs, i.e. for graphs with the type vertex attribute set.

• The name of the graph is printed if there is one, i.e. if the name graph attribute is set.

• 5 6 : The numbers denote the number of vertices and edges.

• attr:name : The attributes of the graph are listed, separated by a comma.

• (v/c) : The kind of attribute - graph (“g”), vertex (“v”) of edge (“e”) is denoted and the type of the attribute as well, character (“c”), numeric (“n”), logical (“l”) or other (“x”)