ggnet was created to do network visualization using the ggplot2 package in R. It is intended to create prettier network visualizations than base R graphics, with an array of color themes and attributes, such as node size, color, shape, and directed/undirected edges. It is a work-in-progress.

Currently, ggnet consists of two R functions, but will (hopefully) be turned into an actual package at some point. ggnet is now an R package hosted on GitHub. To install, you can do the following:

library(devtools)
install_github('mhoover/ggnet/ggnet')

The actual ggnet function requires input data to be a network-class object from the statnet package. Most types of network data, including edgelists and matrices, can be converted to an network class object with little trouble.

library(statnet)

d <- data.frame(sender = c(rep(1, 4), rep(2, 3), rep(3, 4), rep(4, 1)),
    receiver = c(sample(2:5, 4), sample(c(1, 3:5), 3), sample(c(1:2, 4:5),
    4), sample(c(1:3, 5), 1)))

net <- network(d)

At a minimum, the ggnet function only needs a network object as input data; the function defaults to an undirected network.

ggnet(net)

However, there are a robust set of options to improve the aesthetics of the network visualization. These include:

• direct: Boolean value indicating whether or not the network is directed or not.
  • Default is FALSE.
  • If TRUE, arrows will be added to the edges indicating sender/receiver.
• color: Vertex attribute from network-class object (indicated in quotations, e.g., 'age').
  • Default is NULL.
  • Should be inputted as a string.
  • Indicates nodes should be colored based on the age attribute of the node.
• names: Vertex attribute from network-class object (indicated in quotations, e.g., 'vertex.names').
  • Default is NULL.
  • Should be inputted as a string.
  • Indicates nodes should be labeled with the value of the vertex.names attribute (appears as a label directly above the node).
• shape: Vertex attribute from network-class object (indicated in quotations, e.g., 'gender').
  • Default is NULL.
  • Should be inputted as a string.
  • Indicates nodes should be shaped (i.e., circle, triangle, square, etc.) based on the gender attribute of the node.
• size: Vertex attribute from network-class object (indicated in quotations, e.g., 'test.score').
  • Default is NULL.
  • Should be inputted as a string.
  • Indicates nodes should be sized (i.e., smaller/larger) based on the test.score attribute of the node.
• edge.val: Attribute to make edges differentially transparent, based on value.
  • Default is NULL.
  • Should be inputted as a string.
  • It will convert the edge transparency from highly transparent (small value in matrix) to opaque (high value in matrix).
• title: Provide a title to the visualization.
  • Default is NULL.
  • Should be inputted as a string.
• legend: Boolean value to display legend of node/edge attributes used.
  • Default is FALSE.
  • If set to TRUE and with no attributes used, then it is ignored.
• coords: Sets placement of nodes in a specified location.
  • Default is NULL.
  • This parameter should be a data frame of x/y coordinates.
  • Graph algorithms use force-directed placement of nodes, starting with a random value. To achieve consistent placement of nodes for the same networks over time, then specifying coords is advised; otherwise, each time the graph is produced, nodes will be in a different place in space.
  • Specified, reusable coordinates for a network can be created with the coord.place function.
• layout: The type of graph layout used in visualization.
  • Default is 'fruchtermanreingold'.
  • Other (common) options include 'kamadakawai', 'rmds', and 'eigen'.
• plot.layout: Default is NULL; only used for certain algorithm layouts. See gplot.layout for more details.
• palette: Identifies the ggplot2 palatte to use when plotting.
  • Default is 'Set1'.
  • See ggplot2 color theme options for more information.
• gradient: Boolean value for whether or not the color attribute should be treated continuously (i.e., as a gradient) or categorically.
  • Default is FALSE.
  • If TRUE, color attribute will be displayed as a gradient on red/blue spectrum.
• alpha: Numeric value indicating the level of transparency in color.
  • Default is 1.
  • Ranges from 0 (fully transparent) to 1 (opaque).

ggnet(net, direct = TRUE, title = 'Network graph with attributes',
    names = 'vertex.names')

An example network is included with various node (vertex) attributes that can be used to modify the visualization. It is a network-class object in R and will require the statnet (or network) package to be able to properly access its data. Working with network-class objects can be a little tricky, so please refer to the manual on CRAN.

1. With directed graphs, the arrow ends on edges are parially obscured/hidden by the nodes.
2. Input data is limited to network-class objects at the current time.

The underlying graphing capabilities make extensive use of ggplot2 therefore, knowledge of ggplot2 is helpful in terms of developing new features or tweaking existing ones. Help on ggplot2 is available here. For more information, contact matthew.a.hoover at gmail.com.