Animating vertices of a graph with gganimate and ggraph

gg_epi.R

library(tidyverse)
library(igraph)
library(ggraph)
library(gganimate)
library(ggforce)

#File at https://dl.dropbox.com/s/hxmsut19lelgw33/epinetwork.rds
episim <- readRDS("epinetwork.rds") # Saved is the simulation data and an adjacency matrix for the network
# Create an undirected graph from this matrix
ign <- graph_from_adjacency_matrix(episim$network > 0, "undirected")

# Create a layout from the network, attach the x/y values to the simulation data
set.seed(1)
layout <- layout_with_fr(ign) %>% as.data.frame() %>% rename(x=V1, y=V2)
sim1 = episim$simulation %>% 
  group_by(time) %>% 
  mutate(x =layout$x, y=layout$y) %>% 
  group_by() 

sim_end = filter(sim1, time==100) # A single time point for use for background

plot <- ggraph(ign, 'manual', node.positions=layout) + 
  geom_edge_arc(curvature = 0.1, edge_colour='grey40') +
  geom_node_point(data=sim_end, mapping=aes(x=x, y=y), #white bg for the nodes
                  shape=21, size=5, stroke=1,          #to hide the edges beind
                  color="white", fill="white") +       #them
  geom_node_point(data=sim1,
                  mapping=aes(x=x, y=y, fill= (I > 0), alpha=S, frame=time),
                  shape=21, size=5, stroke=1, color="grey10") + 
  scale_fill_manual(breaks=c(0, 1), values=c("black", "red")) +
  scale_alpha_continuous(range=c(0,1)) +
  ggforce::theme_no_axes() +
  theme(legend.position="none",
        panel.border = element_blank())

animation::ani.options(interval=0.1)
gg_animate(plot, 'epi_animation.gif', title_frame = FALSE)