Smooth passage from one graph to another - r

Question

Consider the two following graphs
require(ggplot2)
set.seed(5276)
my_mtcars = mtcars
my_mtcars$rand = rnorm(nrow(mtcars))
ggplot(my_mtcars, aes(rand, mpg)) + geom_point()
ggplot(my_mtcars, aes(wt, mpg)) + geom_point()
I would like to make a movie (or any animated picture that could easily be introduced in a .ppt) that would make a smooth passage from the first graph toward the second. During the passage, we would see the dots smoothly move horizontally to reach their destination. The x-axis scale and label should also appear (eventually smoothly).
I would try to create many .png that are intermediate pictures and then make a gif out of it using ImageMagick (Bash) but I am pretty sure there should be a better solution. I used ggplot2 to produce the plots but I am not strict on that. Here is what I tried for the moment
IntFormat = function(x,nbdigits=0){
cx = paste0(x)
l = length(strsplit(cx,"")[[1]])
if (nbdigits < l){nbdigits = l; print("WARNING: Parameter `nbdigits` too small")}
before = paste(rep("0",nbdigits-l), collapse="")
paste0(before, cx)
}
SmoothGraph = function(x1, x2, y1, y2, times = "NOTSET", ...){
path = "/Users/remi/Desktop/"
if (times == "NOTSET") {
times = c(seq(0,0.1,length.out=10), seq(0,0.2, length.out=5), seq(0.2,0.8, length.out=6), seq(0.8,0.9, length.out=5), seq(0.9,1,length.out=10))
}
nbdigits = length(times)
count = 0
x1_rel = x1 / (max(x1) - min(x1))
x1_rel = x1_rel - max(x1_rel) + 1
x2_rel = x2 / (max(x2) - min(x2))
x2_rel = x2_rel - max(x2_rel) + 1
y1_rel = y1 / (max(y1) - min(y1)) - min(y1)
y1_rel = y1_rel - max(y1_rel) + 1
y2_rel = y2 / (max(y2) - min(y2)) - min(y2)
y2_rel = y2_rel - max(y2_rel) + 1
x_diff = x2_rel - x1_rel
y_diff = y2_rel - y1_rel
for (time in times){
count = count + 1
xtmp = x1_rel + x_diff * time
ytmp = y1_rel + y_diff * time
print(count)
png(paste0(path, "SmoothGraph_", IntFormat(count, nbdigits=nbdigits), ".png"))
plot(x=xtmp, y=ytmp, ...)
dev.off()
}
system (command="
cd /Users/remi/Desktop/
convert SmoothGraph_*.png -delay 1 SmoothGraph.gif
rm SmoothGraph_*.png
")
}
SmoothGraph(x1=rnorm(12), y1=mtcars$mpg , x2 = mtcars$wt, y2=mtcars$mpg)

Answer 1

This seems like a good fit for the animation package. You could do something like this. First, define a function that can interpolate between the two plots
framedata<-function(x) {
subset(transform(my_mtcars,
x=rand + x*(wt-rand),
y=mpg
), select=c(x,y))
}
Then you can animate them with
library(animation)
frame <- seq(0, 1, length.out=20)
saveGIF(lapply(frame, function(f) {
print( ggplot(framedata(f), aes(x, y)) + geom_point() )
}), "go.gif", interval = 0.05, loop=1)
This will create a 20 frame animation with a .05 second delay between frames that plays once.