# Author: Jeff Hemsley jhemsley at uw dot edu

# Created: Nov 20 2012

#

# File generates random graph with random dates and creates set of pngs for animation

#Load igraph

library(igraph)

# igraph has many nifty ways to generate random graphs. :-)

start.nodes <- 2

total.nodes <- 500

g <- erdos.renyi.game(start.nodes, 1/2, directed=T)

g <- barabasi.game(total.nodes, start.graph=g, out.pref=T, directed=T, out.seq=rep(2, total.nodes - start.nodes))

# make a layout and set the x & y attributes of the graph vertices

l <- layout.fruchterman.reingold(g)

V(g)$x <- l[,1]

V(g)$y <- l[,2]

# since I'm using a random graph, i want to use random dates for this example

start.date <- as.POSIXct(strptime('2012-01-01 07:00:00', '%Y-%m-%d %H:%M:%S'))

end.date <- as.POSIXct(strptime('2012-01-07 07:00:00', '%Y-%m-%d %H:%M:%S'))

possible.dates <- seq.POSIXt(start.date, end.date, by="hour")

num.time.steps <- length(possible.dates) # we use later for the loop.

# now we need to associate dates with links and I use sample with replace=T

num.edges <- ecount(g)

E(g)$date <- sample(possible.dates, num.edges, replace=T)

E(g)$width <- 2

# these are some initial edge and vertex settings.

# Note that I set a value for red, green and blue between 0 and 255,

# an alpha, or transparency value of 0 making all objects transparent

E(g)$red <- 255

E(g)$green <- 140

E(g)$blue <- 0

E(g)$alpha <- 0

# then I give a default color just so the attribute exists for later.

E(g)$color <- "black"

V(g)$red <- 95

V(g)$green <- 158

V(g)$blue <- 160

V(g)$alpha <- 0

V(g)$color <- "black"

# season to taste

V(g)$size <- 5

V(g)$frame.color <- NA

V(g)$label <- ""

# in this example I am using a look back of 12 frames for the fade out

# so, over 12 movie frames the links and vertices get more and more

# transparent.

look.back.default <- 12

alpha.vec.default <- round(seq(0, 255, length=look.back.default + 1),0)

alpha.vec.length <- length(alpha.vec.default)

# workhorse loop

for (time.step in 1:num.time.steps) {

# look.back needs to be altered at the early part of the animation

look.back <- time.step - look.back.default

if (look.back < 0) {

look.back <- 1

}

date.fade.index <- look.back:time.step

date.fade.index.length <- length(date.fade.index)

# we always want to set the newest edge/vertex alpha last and we

# we always want it to be opaque. But if look.back is greater than

# available time steps we need to shorten the alpha vector

alpha.vec <- alpha.vec.default

if ((alpha.vec.length - date.fade.index.length) > 0) {

alpha.vec <- alpha.vec[-(1:(alpha.vec.length - date.fade.index.length))]

}

# for each look.back time step we set alpha for edges/vertices

# with those time stamps. Some time steps may have no links or

# vertices, some have many. Do the newest last so that they don't

# get down-graded if they show up more than once in the fade out

# period

for (j in 1:length(date.fade.index)) {

active.edges <- which(E(g)$date == possible.dates[date.fade.index[j]])

if (length(active.edges) > 0) {

E(g)[active.edges]$alpha <- alpha.vec[j]

V(g)[from(E(g)[active.edges])]$alpha <- alpha.vec[j]

V(g)[to(E(g)[active.edges])]$alpha <- alpha.vec[j]

}

}

# now make sure all edge/vertext colors are set with whatever their alphas are

E(g)$color <- rgb(red=E(g)$red, green=E(g)$green

, blue=E(g)$blue, maxColorValue=255, alpha=E(g)$alpha)

V(g)$color <- rgb(V(g)$red, V(g)$green, V(g)$blue, V(g)$alpha, maxColorValue=255)

# file names should be the same except with an incremented number.

# many other R-animation authors use ffmpeg

out.file.name <- paste("/home/jeff/testplot/NetAnimation_", time.step, ".png", sep="")

png(out.file.name, width=640, height=480)

plot.igraph(g, edge.arrow.size=0, edge.arrow.width=0, edge.curved = .5, main="")

dev.off()

}