combine multiple plots to a gif - r

Question

Im trying to use the caTools package to combine multiple plots into a gif.
My basic code looks like :
for( i in 1:100){
plot(....) // plots few points and lines, changes slightly with each i
}
I would like to combine these to a gif to see the "evolution" of the plot.
However for write.gif() from caTools, I need to give an image as an input.
For each i, how do I convert the plot into an image without
saving to disc as an intermediate step
depending on ImageMagick or similar external dependencies.
Please feel free to point out if this is a duplicate. [ Creating a Movie from a Series of Plots in R doesnt seem to answer this ]
EDIT: Basically this requires us to convert a plot to a matrix. Since this very likely happens every time someone saves a plot, it should not be very difficult. However Im not able to get hold of how to exactly do this.

Answer 1

I suggest using the animation package and ImageMagick instead:
library(animation)
## make sure ImageMagick has been installed in your system
saveGIF({
for (i in 1:10) plot(runif(10), ylim = 0:1)
})
Otherwise you could try it in the veins of this (plenty of room for optimization):
library(png)
library(caTools)
library(abind)
# create gif frames and write them to pngs in a temp dir
dir.create(dir <- tempfile(""))
for (i in 1:8) {
png(file.path(dir, paste0(sprintf("%04d", i), ".png")))
plot(runif(10), ylim = 0:1, col = i)
dev.off()
}
# read pngs, create global palette, convert rasters to integer arrays and write animated gif
imgs <- lapply(list.files(dir, full.names = T), function(fn) as.raster(readPNG(fn)))
frames <- abind(imgs, along = 3) # combine raster pngs in list to an array
cols <- unique(as.vector(frames)) # determine unique colors, should be less then 257
frames <- aperm(array(match(frames, cols) - 1, dim = dim(frames)), c(2,1,3)) # replace rgb color codes (#ffffff) by integer indices in cols, beginning with 0 (note: array has to be transposed again, otherwise images are flipped)
write.gif(
image = frames, # array of integers
filename = tf <- tempfile(fileext = ".gif"), # create temporary filename
delay = 100, # 100/100=1 second delay between frames
col = c(cols, rep("#FFFFFF", 256-length(cols))) # color palette with 256 colors (fill unused color indices with white)
)
# open gif (windows)
shell.exec(tf)

Answer 2

Is that what you are looking for?
library(ggplot2)
a <- 0:10
df <- data.frame(a=a,b=a)
steps <-function(end){
a <- ggplot(df[1:end,], aes(a,b)) +
geom_point() +
scale_x_continuous(limits=c(0,10)) +
scale_y_continuous(limits=c(0,10))
print(a)
}
gif <- function() {
lapply(seq(1,11,1), function(i) {
steps(i)
})
}
library(animation)
saveGIF(gif(), interval = .2, movie.name="test.gif")

Answer 3

I liked #ttlngr's answer but I wanted something a bit simpler (it still uses ImageMagick).
saveGIF({
for (i in 1:10){
a <- ggplot(df[1:i,], aes(a,b)) +
geom_point() +
scale_x_continuous(limits=c(0,10)) +
scale_y_continuous(limits=c(0,10))
print(a)}
}, interval = .2, movie.name="test.gif")