Animate the process of adding layers to a ggplot2 plot

Question

I am starting to get familiar with gganimate, but I want to extend my gifs further.

For instance, I can throw a frame on one variable in gganimate but what if I want to animate the process of adding entirely new layers/geoms/variables?

Here's a standard gganimate example:

library(tidyverse)
library(gganimate)

p <- ggplot(mtcars, aes(x = hp, y = mpg, frame = cyl)) +
    geom_point()

gg_animate(p)

But what if I want the gif to animate:

# frame 1
ggplot(mtcars, aes(x = hp, y = mpg)) +
    geom_point()

# frame 2
ggplot(mtcars, aes(x = hp, y = mpg)) +
    geom_point(aes(color = factor(cyl)))

# frame 3
ggplot(mtcars, aes(x = hp, y = mpg)) +
    geom_point(aes(color = factor(cyl), size = wt))

# frame 4
ggplot(mtcars, aes(x = hp, y = mpg)) +
    geom_point(aes(color = factor(cyl), size = wt)) +
    labs(title = "MTCARS")

How might this be accomplished?

Answer 1

You can manually add a frame aesthetic to each layer, though it will include the legends for all of the frames immediately (Intentionally, I believe, to keep ratios/margins, etc. correct:

saveAnimate <-
  ggplot(mtcars, aes(x = hp, y = mpg)) +
  # frame 1
  geom_point(aes(frame = 1)) +
  # frame 2
  geom_point(aes(color = factor(cyl)
                 , frame = 2)
             ) +
  # frame 3
  geom_point(aes(color = factor(cyl), size = wt
                 , frame = 3)) +
  # frame 4
  geom_point(aes(color = factor(cyl), size = wt
                 , frame = 4)) +
  # I don't think I can add this one
  labs(title = "MTCARS")

gg_animate(saveAnimate)

If you want to be able to add things yourself, and even see how legends, titles, etc. move things around, you may need to step back to a lower-level package, and construct the images yourself. Here, I am using the animation package which allows you to loop through a series of plots, with no limitations (they need not be related at all, so can certainly show things moving the plot area around. Note that I believe this requires ImageMagick to be installed on your computer.

p <- ggplot(mtcars, aes(x = hp, y = mpg))

toSave <- list(
  p + geom_point()
  , p + geom_point(aes(color = factor(cyl)))
  , p + geom_point(aes(color = factor(cyl), size = wt))
  , p + geom_point(aes(color = factor(cyl), size = wt)) +
    labs(title = "MTCARS")
)

library(animation)

saveGIF(
  {lapply(toSave, print)}
  , "animationTest.gif"
 )

Answer 2

The gganimate commands in the earlier answers are deprecated as of 2021 and won't accomplish OP's task.

Building on Mark's code, you can now simply create a static ggplot object with multiple layered geoms and then add the gganimate::transition_layers function to create an animation that transitions from layer to layer within the static plot. Tweening functions like enter_fade() and enter_grow() control how elements change into and out of frames.

library(tidyverse)
library(gganimate)

anim <- ggplot(mtcars, aes(x = hp, y = mpg)) +
  # Title
  labs(title = "MTCARS") +
  # Frame 1
  geom_point() +
  # Frame 2  
  geom_point(aes(color = factor(cyl))) +
  # Frame 3
  geom_point(aes(color = factor(cyl), size = wt)) +
  # gganimate functions
  transition_layers() + enter_fade() + enter_grow()

# Render animation
animate(anim)