Positioning nodes and edges in network graph using ggraph/ggplot2 - r

Question

I'm trying to plot a network with ggraph and I'd like to add a circle around the graph, with the edges and nodes lying centered inside the circle.
Drawing the circle works just fine with the following code (adapted from Draw a circle with ggplot2)
gg_circle <- function(r, xc, yc, color = "black", fill = NA, lty = NA, size = NA, ...) {
x <- xc + r*cos(seq(0, pi, length.out = 100))
ymax <- yc + r*sin(seq(0, pi, length.out = 100))
ymin <- yc + r*sin(seq(0, -pi, length.out = 100))
annotate("ribbon", x = x, ymin = ymin, ymax = ymax,
color = color, fill = fill, lty = lty, size = size, ...)
}
But I can't manage to match the position of the network layer(s) with the position of the circle, which results in both nodes and edges lying partially outside the circle:
That's the crucial part of the code as it is right now (using highschool from ggraph as an example dataset for reproducibility purposes):
library(ggraph)
library(igraph)
graph <- graph_from_data_frame(highschool)
ggraph(graph, layout = "fr") +
geom_edge_link() +
geom_node_point() +
geom_node_text(aes(label = name),
check_overlap = TRUE, repel = TRUE,
nudge_x = 0.1, nudge_y = 0.1) +
gg_circle(r = 11, xc = 0, yc = 0, lty = 1, size = 0.2) +
theme(axis.ticks.length = unit(0, "cm"),
legend.position = "none",
plot.margin = unit(c(0, 0, 0, 0), "cm"),
panel.spacing = unit(c(0, 0, 0, 0), "cm")) +
coord_fixed()
Any ideas or suggestions on how to fix this? Thanks in advance!

Answer 1

I would try to use the node positions to find acceptable values for r, xc, and yc.
Step 1. Create plot (without the circle):
set.seed(9) # for reproducibility
p <- ggraph(graph, layout = "fr") +
geom_edge_link() +
geom_node_point() +
geom_node_text(aes(label = name),
check_overlap = TRUE,
repel = TRUE,
nudge_x = 0.1,
nudge_y = 0.1) +
theme(axis.ticks.length = unit(0, "cm"),
legend.position = "none",
plot.margin = unit(c(0, 0, 0, 0), "cm"),
panel.spacing = unit(c(0, 0, 0, 0), "cm")) +
coord_fixed()
Step 2. Get data from the plot's geom_node_point() layer (the 2nd layer in this case). Modify the gg_circle code to take this dataframe as input, & calculate the appropriate circle centre coordinates / radius:
p.positions <- layer_data(p, i = 2L)
gg_circle_from_position <- function(data,
color = "black", fill = NA,
lty = NA, size = NA, ...){
coord.x <- data[, 'x']
coord.y <- data[, 'y']
xc = mean(range(coord.x))
yc = mean(range(coord.y))
r = max(sqrt((coord.x - xc)^2 + (coord.y - yc)^2)) * 1.05
# expand radius by 5% so that no node sits exactly on the line;
# increase from 1.05 to some larger number if more buffer is desired.
# no change to this part
x <- xc + r*cos(seq(0, pi, length.out = 100))
ymax <- yc + r*sin(seq(0, pi, length.out = 100))
ymin <- yc + r*sin(seq(0, -pi, length.out = 100))
annotate("ribbon", x = x, ymin = ymin, ymax = ymax,
color = color, fill = fill, lty = lty, size = size, ...)
}
Step 3. Add circle to plot:
p + gg_circle_from_position(data = p.positions, lty = 1, size = 0.2)