/dʒiː.dʒɪˈrɑːf/ (or g-giraffe)
ggraph is an extension of ggplot2
aimed at supporting relational data structures such as networks, graphs, and trees. While it builds upon the foundation of ggplot2
and its API it comes with its own self-contained set of geoms, facets, etc., as well as adding the concept of layouts to the grammar.
library(ggraph)
#> Loading required package: ggplot2
library(igraph)
#>
#> Attaching package: 'igraph'
#> The following objects are masked from 'package:stats':
#>
#> decompose, spectrum
#> The following object is masked from 'package:base':
#>
#> union
# Create graph of highschool friendships
graph <- graph_from_data_frame(highschool)
V(graph)$Popularity <- degree(graph, mode = 'in')
# plot using ggraph
ggraph(graph, layout = 'kk') +
geom_edge_fan(aes(alpha = ..index..), show.legend = FALSE) +
geom_node_point(aes(size = Popularity)) +
facet_edges(~year) +
theme_graph(foreground = 'steelblue', fg_text_colour = 'white')
ggraph
builds upon three core concepts that are quite easy to understand:
- The Layout defines how nodes are placed on the plot, that is, it is a conversion of the relational structure into an x and y value for each node in the graph.
ggraph
has access to all layout functions avaiable inigraph
and furthermore provides a large selection of its own, such as hive plots, treemaps, and circle packing. - The Nodes are the connected entities in the relational structure. These can be plotted using the
geom_node_*()
family of geoms. Some node geoms make more sense for certain layouts, e.g.geom_node_tile()
for treemaps and icicle plots, while others are more general purpose, e.g.geom_node_point()
. - The Edges are the connections between the entities in the relational structure. These can be visualized using the
geom_edge_*()
family of geoms that contain a lot of different edge types for different scenarios. Sometimes the edges are implied by the layout (e.g. with treemaps) and need not be plotted, but often some sort of line is warranted.
All of the tree concepts have been discussed in detail in dedicated blog posts that are also available as vignettes in the package. Please refer to these for more information.
There are many different ways to store and work with relational data in R. Out of the box ggraph
comes with first-class support for igraph
and dendrogram
objects, while network
and hclust
objects are supported through automatic conversion to one of the above. Users can add support for other data structures by writing a set of methods for that class. If this is of interest it is discussed further in layouts.
ggraph
is available through CRAN and can be installed with install_packages('ggraph')
. The package is under active development though and the latest set of features can be obtained by installing from this repository using devtools
devtools::install_github('thomasp85/ggraph')
ggraph
is not the only package to provide some sort of support for relational data in ggplot2
, though I'm fairly certain that it is the most ambituous. ggdendro
provides support for dendrogram
and hclust
objects through conversion of the structures into line segments that can then be plotted with geom_segment()
. ggtree
provides more extensive support for all things tree-related, though it lacks some of the layouts and edge types that ggraph
offers (it has other features that ggraph
lacks though). For more standard hairball network plots ggnetwork
, geomnet
, and GGally
all provide some functionality though none of them are as extensive in scope as ggraph
.