igraph (version 0.6.6)

attributes: Graph, vertex and edge attributes

Description

Attributes are associated values belonging to a graph, vertices or edges. These can represent some property, like data about how the graph was constructed, the color of the vertices when the graph is plotted, or simply the weights of the edges in a weighted graph.

Usage

get.graph.attribute(graph, name)
set.graph.attribute(graph, name, value)
remove.graph.attribute(graph, name)
get.vertex.attribute(graph, name, index=V(graph))
set.vertex.attribute(graph, name, index=V(graph), value)
remove.vertex.attribute(graph, name)
get.edge.attribute(graph, name, index=E(graph))
set.edge.attribute(graph, name, index=E(graph), value)
remove.edge.attribute(graph, name)

Arguments

graph

The graph object to work on. Note that the original graph is never modified, a new graph object is returned instead; if you don't assign it to a variable your modifications will be lost! See examples below.

name

Character constant, the name of the attribute.

index

Numeric vector, the ids of the vertices or edges. It is not recycled, even if value is longer.

value

Numeric vector, the new value(s) of the attributes, it will be recycled if needed.

Value

• get.graph.attribute, get.vertex.attribute and get.edge.attribute return an R object, or a list of R objects if attributes of more vertices/edges are requested.

  set.graph.attribute, set.vertex.attribute, set.edge.attribute, and also remove.graph.attribute, remove.vertex.attribute and remove.edge.attribute return a new graph object with the updates/removes performed.

  list.graph.attributes, list.vertex.attributes and list.edge.attributes return a character vector, the names of the attributes present.

concept

Vertex/edge/graph attributes

Details

There are three types of attributes in igraph: graph, vertex and edge attributes. Graph attributes are associated with graph, vertex attributes with vertices and edge attributes with edges.

Examples for graph attributes are the date when the graph data was collected or other types of memos like the type of the data, or whether the graph is a simple graph, ie. one without loops and multiple edges.

Examples of vertex attributes are vertex properties, like the vertex coordinates for the visualization of the graph, or other visualization parameters, or meta-data associated with the vertices, like the gender and the age of the individuals in a friendship network, the type of the neurons in a graph representing neural circuitry or even some pre-computed structual properties, like the betweenness centrality of the vertices.

Examples of edge attributes are data associated with edges: most commonly edge weights, or visualization parameters.

In recent igraph versions, arbitrary R objects can be assigned as graph, vertex or edge attributes. Some igraph functions use the values or graph, vertex and edge attributes if they are present but this is not done in the current version very extensively. Expect more in the (near) future.

Graph attributes can be created with the set.graph.attribute function, and removed with remove.graph.attribute. Graph attributes are queried with get.graph.attribute and the assigned graph attributes are listed with list.graph.attributes.

There is a simpler notation for using graph attributes: the $ operator. It can be used both to query and set graph attributes, see an example below. The functions for vertex attributes are set.vertex.attribute, get.vertex.attribute, remove.vertex.attribute and list.vertex.attributes and for edge attributes they are set.edge.attribute, get.edge.attribute, remove.edge.attribute and list.edge.attributes. There is however a (syntactically) much simpler way to handle vertex and edge attribute by using vertex and edge selectors, it works like this: V(g) selects all vertices in a graph, and V(g)$name queries the name attribute for all vertices. Similarly is vs is a vertex set vs$name gives the values of the name attribute for the vertices in the vertex set.

This form can also be used to set the values of the attributes, like the regular R convention: V(g)$color <- "red" It works for vertex subsets as well: V(g)[1:5]$color <- "green"

The notation for edges is similar: E(g) means all edges E(g)$weight is the weight attribute for all edges, etc.

See also the manual page for iterators about how to create various vertex and edge sets.

See Also

print.igraph can print attributes. See attribute.combination for details on how igraph combines attributes if several vertices or edges are mapped into one.

Examples

g <- graph.ring(10)
g <- set.graph.attribute(g, "name", "RING")
# It is the same as
g$name <- "RING"
g$name

g <- set.vertex.attribute(g, "color", value=c("red", "green"))
get.vertex.attribute(g, "color")

g <- set.edge.attribute(g, "weight", value=runif(ecount(g)))
get.edge.attribute(g, "weight")

# The following notation is more convenient

g <- graph.star(10)

V(g)$color <- c("red", "green")
V(g)$color

E(g)$weight <- runif(ecount(g))
E(g)$weight

print(g, g=TRUE, v=TRUE, e=TRUE)