Drawing graphs {igraph} | R Documentation |
The common bits of the three plotting functions
plot.igraph
, tkplot
and rglplot
are discussed in
this manual page
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.
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 no 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.options
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...)
Vertex parameters first, note that the ‘vertex.
’ prefix
needs to be added if they are used as an argument or when setting via
igraph.options
. 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.)
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.
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.
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.
If you don't want (some) vertices to have any color, supply
NA
as the color name.
The default value is “SkyBlue2
”.
The color of the frame of the vertices, the same formats are allowed as for the fill color.
If you don't want vertices to have a frame, supply NA
as
the color name.
By default it is “black”.
The shape of the vertex, currently
“circle
”, “square
”,
“csquare
”, “rectangle
”,
“crectangle
”, “vrectangle
”,
“pie
” (see vertex.shape.pie),
‘sphere
’, 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 and vertex.shape.pie
for using pie charts as
vertices.
The “sphere
” vertex shape plots vertices as 3D
ray-traced spheres, in the given color and size. This produces a
raster image and it is only supported with some graphics
devices. On some devices raster transparency is not supported and
the spheres do not have a transparent background. See
dev.capabilities
and the ‘rasterImage
’
capability to check that your device is supported.
By default vertices are drawn as circles.
The vertex labels. They will be converted to
character. Specify NA
to omit vertex labels.
The default vertex labels are the vertex ids.
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’.
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.
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.
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.
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
.
The color of the labels, see the color
vertex parameter discussed earlier for the possible values.
The default value is black
.
Edge parameters require to add the ‘edge.
’ prefix when
used as arguments or set by igraph.options
. The edge
parameters:
The color of the edges, see the color
vertex
parameter for the possible values.
By default this parameter is darkgrey
.
The width of the edges.
The default value is 1.
The size of the arrows. Currently this is a constant, so it is the same for every edge. If a vector is submitted then only the first element is used, ie. if this is taken from an edge attribute then only the attribute of the first edge is used for all arrows. This will likely change in the future.
The default value is 1.
The width of the arrows. Currently this is a constant, so it is the same for every edge. If a vector is submitted then only the first element is used, ie. if this is taken from an edge attribute then only the attribute of the first edge is used for all arrows. This will likely change in the future.
This argument is currently only used by plot.igraph
.
The default value is 1, which gives the same width as before this option appeared in igraph.
The line type for the edges. Almost the same format is
accepted as for the standard graphics par
,
0 and “blank” mean no edges, 1 and “solid” are for
solid lines, the other possible values are: 2 (“dashed”),
3 (“dotted”), 4 (“dotdash”), 5 (“longdash”),
6 (“twodash”).
tkplot
also accepts standard Tk line type strings,
it does not however support “blank” lines, instead of type
‘0’ type ‘1’, ie. solid lines will be drawn.
This argument is ignored for rglplot
.
The default value is type 1, a solid line.
The edge labels. They will be converted to
character. Specify NA
to omit edge labels.
Edge labels are omitted by default.
Font family of the edge labels. See the vertex parameter with the same name for the details.
The font for the edge labels. See the corresponding vertex parameter discussed earlier for details.
The font size for the edge labels, see the corresponding vertex parameter for details.
The color of the edge labels, see the
color
vertex parameters on how to specify colors.
Specifies whether to draw curved edges, or not. This can be a logical or a numeric vector or scalar.
First the vector is replicated to have the same length as the
number of edges in the graph. Then it is interpreted for each edge
separately. A numeric value specifies the curvature of the edge;
zero curvature means straight edges, negative values means the
edge bends clockwise, positive values the opposite. TRUE
means curvature 0.5, FALSE
means curvature zero.
By default the vector specifying the curvatire is calculated via a
call to the autocurve.edges
function. This function makes
sure that multiple edges are curved and are all visible. This
parameter is ignored for loop edges.
The default value is FALSE
.
This parameter is currently ignored by rglplot
.
This parameter can be used to specify for which edges should arrows be drawn. If this parameter is given by the user (in either of the three ways) then it specifies which edges will have forward, backward arrows, or both, or no arrows at all. As usual, this parameter can be a vector or a scalar value. It can be an integer or character type. If it is integer then 0 means no arrows, 1 means backward arrows, 2 is for forward arrows and 3 for both. If it is a character vector then “<” and “<-” specify backward, “>” and “->” forward arrows and “<>” and “<->” stands for both arrows. All other values mean no arrows, perhaps you should use “-” or “–” to specify no arrows.
Hint: this parameter can be used as a ‘cheap’ solution for drawing “mixed” graphs: graphs in which some edges are directed some are not. If you want do this, then please create a directed graph, because as of version 0.4 the vertex pairs in the edge lists can be swapped in undirected graphs.
By default, no arrows will be drawn for undirected graphs, and for directed graphs, an arrow will be drawn for each edge, according to its direction. This is not very surprising, it is the expected behavior.
Gives the angle in radian for plotting loop
edges. See the label.dist
vertex parameter to see how this
is interpreted.
The default value is 0.
Gives the second angle in radian for plotting
loop edges. This is only used in 3D, loop.angle
is enough
in 2D.
The default value is 0.
Other parameters:
Either a function or a numeric matrix. It specifies how the vertices will be placed on the plot.
If it is a numeric matrix, then the matrix has to have one line for
each vertex, specifying its coordinates. The matrix should have at
least two columns, for the x
and y
coordinates, and
it can also have third column, this will be the z
coordinate for 3D plots and it is ignored for 2D plots.
If a two column matrix is given for the 3D plotting function
rglplot
then the third column is assumed to be 1 for
each vertex.
If layout
is a function, this function will be called with the
graph
as the single parameter to determine the
actual coordinates. The function should return a matrix with two
or three columns. For the 2D plots the third column is ignored.
The default value is layout.random
, ie. a function
returning with 2D random placement.
The amount of empty space below, over, at the left and right of the plot, it is a numeric vector of length four. Usually values between 0 and 0.5 are meaningful, but negative values are also possible, that will make the plot zoom in to a part of the graph. If it is shorter than four then it is recycled.
rglplot
does not support this parameter, as it can
zoom in and out the graph in a more flexible way.
Its default value is 0.
Logical constant, whether to rescale the coordinates
to the [-1,1]x[-1,1](x[-1,1]) interval. This parameter is not
implemented for tkplot
.
Defaults to TRUE
, the layout will be rescaled.
A numeric constant, it gives the asp
parameter
for plot
, the aspect ratio. Supply 0 here if you
don't want to give an aspect ratio. It is ignored by tkplot
and rglplot
.
Defaults to 1.
Boolean, whether to plot a frame around the graph. It
is ignored by tkplot
and rglplot
.
Defaults to FALSE
.
Gabor Csardi csardi.gabor@gmail.com
plot.igraph
, tkplot
,
rglplot
, igraph.options
## Not run: # 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.options(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") ## End(Not run)