Drawing graphs

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Drawing graphs

The common bits of the three plotting functions plot.igraph, tkplot and rglplot are discussed in this manual page

Keywords
graphs
Details

There are currently three different functions in the igraph package which can draw graph in various ways:

plot.igraph does simple non-interactive 2D plotting to R devices. Actually it is an implementation of the plot generic function, so you can write plot(graph) instead of plot.igraph(graph). As it used the standard R devices it supports every output format for which R has an output device. The list is quite impressing: PostScript, PDF files, XFig files, SVG files, JPG, PNG and of course you can plot to the screen as well using the default devices, or the good-looking anti-aliased Cairo device. See plot.igraph for some more information.

tkplot does interactive 2D plotting using the tcltk package. It can only handle graphs of moderate size, a thousend vertices is probably already too many. Some parameters of the plotted graph can be changed interactively after issuing the tkplot command: the position, color and size of the vertices and the color and width of the edges. See tkplot for details. rglplot is an experimental function to draw graphs in 3D using OpenGL. See rglplot for some more information.

Please also check the examples below.

concept

Visualization

How to specify graphical parameters

There are three ways to give values to the parameters described below, in section 'Parameters'. We give these three ways here in the order of their precedence.

The first method is to supply named arguments to the plotting commands: plot.igraph, tkplot or rglplot. Parameters for vertices start with prefix vertex., parameters for edges have prefix edge., and global parameters have now prefix. Eg. the color of the vertices can be given via argument vertex.color, whereas edge.color sets the color of the edges. layout gives the layout of the graphs.

The second way is to assign vertex, edge and graph attributes to the graph. These attributes have now prefix, ie. the color of the vertices is taken from the color vertex attribute and the color of the edges from the color edge attribute. The layout of the graph is given by the layout graph attribute. (Always assuming that the corresponding command argument is not present.) Setting vertex and edge attributes are handy if you want to assign a given look to a graph, attributes are saved with the graph is you save it with save or in GraphML format with write.graph, so the graph will have the same look after loading it again.

If a parameter is not given in the command line, and the corresponding vertex/edge/graph attribute is also missing then the general igraph parameters handled by igraph.par are also checked. Vertex parameters have prefix vertex., edge parameters are prefixed with edge., general parameters like layout are prefixed with plot. These parameters are useful if you want all or most of your graphs to have the same look, vertex size, vertex color, etc. Then you don't need to set these at every plotting, and you also don't need to assign vertex/edge attributes to every graph.

If the value of a parameter is not specified by any of the three ways described here, its default valued is used, as given in the source code.

Different parameters can have different type, eg. vertex colors can be given as a character vector with color names, or as an integer vector with the color numbers from the current palette. Different types are valid for different parameters, this is discussed in detail in the next section. It is however always true that the parameter can always be a function object in which it will be called with the graph as its single argument to get the proper value of the parameter. (If the function returns another function object that will not be called again...)

The list of parameters

Vertex parameters first, note that the vertex. prefix needs to be added if they are used as an argument or when setting via igraph.par. The value of the parameter may be scalar valid for every vertex or a vector with a separate value for each vertex. (Shorter vectors are recycled.)

  • size
{The size of the vertex, a numeric scalar or vector, in the latter case each vertex sizes may differ. This vertex sizes are scaled in order have about the same size of vertices for a given value for all three plotting commands. It does not need to be an integer number.

The default value is 15. This is big enough to place short labels on vertices.} size2{The other size of the vertex, for some vertex shapes. For the various rectangle shapes this gives the height of the vertices, whereas size gives the width. It is ignored by shapes for which the size can be specified with a single number.

The default is 15. } color{The fill color of the vertex. If it is numeric then the current palette is used, see palette. If it is a character vector then it may either contain named colors or RGB specified colors with three or four bytes. All strings starting with # are assumed to be RGB color specifications. It is possible to mix named color and RGB colors. Note that tkplot ignores the fourth byte (alpha channel) in the RGB color specification.

The default value is SkyBlue2. } frame.color{The color of the frame of the vertices, the same formats are allowed as for the fill color.

By default it is black. } shape{The shape of the vertex, currently circle, square, csquare, rectangle, crectangle, vrectangle and none are supported, and only by the plot.igraph command. none does not draw the vertices at all, although vertex label are plotted (if given). See igraph.vertex.shapes for details about vertex shapes.

By default vertices are drawn as circles. } label{The vertex labels. They will be converted to character. Specify NA to omit vertex labels.

The default vertex labels are the vertex ids. } label.family{The font family to be used for vertex labels. As different plotting commands can used different fonts, they interpret this parameter different ways. The basic notation is, however, understood by both plot.igraph and tkplot. rglplot does not support fonts at all right now, it ignores this parameter completely.

For plot.igraph this parameter is simply passed to text as argument family.

For tkplot some conversion is performed. If this parameter is the name of an exixting Tk font, then that font is used and the label.font and label.cex parameters are ignored complerely. If it is one of the base families (serif, sans, mono) then Times, Helvetica or Courier fonts are used, there are guaranteed to exist on all systems. For the symbol base family we used the symbol font is available, otherwise the first font which has symbol in its name. If the parameter is not a name of the base families and it is also not a named Tk font then we pass it to tkfont.create and hope the user knows what she is doing. The label.font and label.cex parameters are also passed to tkfont.create in this case.

The default value is serif. } label.font{The font within the font family to use for the vertex labels. It is interpreted the same way as the the font graphical parameter: 1 is plain text, 2 is bold face, 3 is italic, 4 is bold and italic and 5 specifies the symbol font.

For plot.igraph this parameter is simply passed to text.

For tkplot, if the label.family parameter is not the name of a Tk font then this parameter is used to set whether the newly created font should be italic and/or boldface. Otherwise it is ignored.

For rglplot it is ignored.

The default value is 1. } label.cex{The font size for vertex labels. It is interpreted as a multiplication factor of some device-dependent base font size.

For plot.igraph it is simply passed to text as argument cex.

For tkplot it is multiplied by 12 and then used as the size argument for tkfont.create. The base font is thus 12 for tkplot.

For rglplot it is ignored.

The default value is 1. } label.dist{ The distance of the label from the center of the vertex. If it is 0 then the label is centered on the vertex. If it is 1 then the label is displayed beside the vertex.

The default value is 0. } label.degree{ It defines the position of the vertex labels, relative to the center of the vertices. It is interpreted as an angle in radian, zero means to the right, and pi means to the left, up is -pi/2 and down is pi/2.

The default value is -pi/4. } label.color{The color of the labels, see the color vertex parameter discussed earlier for the possible values.

The default value is black. }

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itemize

  • layout

item

  • width
  • arrow.size
  • arrow.width
  • lty
  • label
  • label.family
  • label.font
  • label.cex
  • label.color
  • curved
  • arrow.mode
  • loop.angle
  • loop.angle2
  • margin
  • rescale
  • asp
  • frame

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See Also

plot.igraph, tkplot, rglplot, igraph.par

Aliases
  • igraph.plotting
Examples
# plotting a simple ring graph, all default parameters, except the layout
g <- graph.ring(10)
g$layout <- layout.circle
plot(g)
tkplot(g)
rglplot(g)

# plotting a random graph, set the parameters in the command arguments
g <- barabasi.game(100)
plot(g, layout=layout.fruchterman.reingold, vertex.size=4,
     vertex.label.dist=0.5, vertex.color="red", edge.arrow.size=0.5)

# plot a random graph, different color for each component
g <- erdos.renyi.game(100, 1/100)
comps <- clusters(g)$membership
colbar <- rainbow(max(comps)+1)
V(g)$color <- colbar[comps+1]
plot(g, layout=layout.fruchterman.reingold, vertex.size=5, vertex.label=NA)

# plot communities in a graph
g <- graph.full(5) %du% graph.full(5) %du% graph.full(5)
g <- add.edges(g, c(0,5, 0,10, 5,10))
com <- spinglass.community(g, spins=5)
V(g)$color <- com$membership+1
g <- set.graph.attribute(g, "layout", layout.kamada.kawai(g))
plot(g, vertex.label.dist=1.5)

# draw a bunch of trees, fix layout
igraph.par("plot.layout", layout.reingold.tilford)
plot(graph.tree(20, 2))
plot(graph.tree(50, 3), vertex.size=3, vertex.label=NA)
tkplot(graph.tree(50, 2, mode="undirected"), vertex.size=10, vertex.color="green")
Documentation reproduced from package igraph, version 0.5.3, License: GPL (>= 2)

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