[R] igraph tree: increase vertex separation within tier

[Loris Bennett]

Hi,

I am collecting data about network errors and would like to visualise
the results in some sort of graph which reflects the hierarchy of the
components in the network (i.e. core switches are connected to leaf
switches and nodes are connected to leaf switches).

The errors are in file which looks something like this:

--------
2015-07-15;coreswitch01;1;0
2015-07-15;coreswitch01;2;0
2015-07-15;leafswitch01;1;0
2015-07-15;leafswitch01;2;0
2015-07-15;leafswitch01;3;0
2015-07-15;leafswitch01;4;0
2015-07-15;leafswitch01;5;0
2015-07-15;leafswitch02;1;0
2015-07-15;leafswitch02;2;0
2015-07-15;leafswitch02;3;0
2015-07-15;leafswitch02;4;0
2015-07-15;leafswitch02;5;0
2015-07-15;leafswitch02;2;561
2015-07-15;node001;1;0
2015-07-15;node002;1;0
2015-07-15;node003;1;0
2015-07-15;node004;1;3
2015-07-15;node005;1;10529
2015-07-15;node007;1;0
2015-07-15;node008;1;2081
--------

and the topology file, which relates ports to ports and ports to
multiport components, looks something like this:

--------
coreswitch01;coreswitch01_01
coreswitch01;coreswitch01_02
leafswitch01;leafswitch01_01
leafswitch01;leafswitch01_02
leafswitch01;leafswitch01_03
leafswitch01;leafswitch01_04
leafswitch01;leafswitch01_05
leafswitch02;leafswitch02_01
leafswitch02;leafswitch02_02
leafswitch02;leafswitch02_03
leafswitch02;leafswitch02_04
leafswitch02;leafswitch02_05
coreswitch01_01;leafswitch01_01
coreswitch01_02;leafswitch02_01
leafswitch01_02;node001_01
leafswitch01_03;node002_01
leafswitch01_04;node003_01
leafswitch01_05;node004_01
leafswitch02_02;node005_01
leafswitch02_03;node006_01
leafswitch02_04;node007_01
leafswitch02_05;node008_01
--------


I'm plotting the data with the following:

--------
library("igraph")

error_data <- read.csv(file="errors.csv",head=FALSE,sep=";")
colnames(error_data) <- c("datetime","name","portnumber","generic_error");

topo_data <- read.csv(file="topology.csv",head=FALSE,sep=";")
G <-graph.data.frame(topo_data, directed=F)

error_counter <- 'generic_error'
error_counter_max <- max(error_data[,error_counter])

vcolours <- 100 - round(99*error_data[,error_counter]/error_counter_max)
hc100 <- heat.colors(100)
vcolour_values <- hc100[vcolours]

l <- layout_(G,as_tree(root=c(1),rootlevel=c(1)))

plot(G, layout = l, vertex.shape = "rectangle", vertex.color=vcolour_values)
--------

This produces roughly what I want.  However, even with this subset of
the full network, there is quite a lot of overlapping of vertex labels
within the lowest tier.  The full data set has over 100 vertices on the
lowest tier, which causes the labels to become illegible.  I can adjust
the aspect ratio of the plot and/or the canvas, but this doesn't affect
the separation between the vertices.

Does anyone have any advice about how to display such information?
(Completely different approaches also welcome.)

Cheers,

Loris

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