gganimate animate based on both ID and time

Question

I’m quite new to gganimate, and I’m struggling with it quite a bit.

Here is my current animation; each set of lines that appears corresponds to a new participant:

As you may notice, my x axis represents two points in time (Before and After an event). I would therefore like to animate each line, so that a datapoint first appears on “before”, and then traces a path/line to reach the “after” value. All that, while keeping the participant by participant display that I currently have. Is there any way to achieve this ?

Here is my code for the current animation :

library('ggplot2')
library('gifski')
library('gganimate')
library('transformr')

anim <- df %>% ggplot(aes(x = factor(prepost, levels = c("Before", "After")), y = value)) +
  geom_point() +
  geom_line(aes(group = participant), size = 0.8) +
  scale_y_continuous(breaks = seq(10, 50, 5)) +
  scale_color_identity() +
  facet_wrap(~factor(group, levels = c("Positive", "Negative")), ncol = 2) +
  transition_time(participant) +
  shadow_mark(past = T, future = F, size = 0.2, alpha = 0.1) 
animate(anim, fps = 2)

I have tried using transition_reveal() and transition_states(), but with no result, I tried doing the transition using my “prepost” variable, or even an artifically created “time” variable, but everything failed.

Here is a nugget of my dataset to reproduce what I did (it’s from a dataframe in long format) :

df <- structure(list(participant = c(1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 
3, 3, 4, 4, 4, 4, 5, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 
8, 9, 9, 9, 9, 10, 10, 10, 10, 11, 11, 11, 11, 12, 12, 12, 12, 
13, 13, 13, 13, 14, 14, 14, 14, 15, 15, 15, 15, 16, 16, 16, 16, 
17, 17, 17, 17, 18, 18, 18, 18, 19, 19, 19, 19, 20, 20, 20, 20, 
21, 21, 21, 21, 22, 22, 22, 22, 23, 23, 23, 23, 24, 24, 24, 24, 
25, 25, 25, 25), variable = c("POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post", "POS_pre", "NEG_pre", 
"POS_post", "NEG_post"), value = c(24, 23, 26, 13, 
22, 11, 38, 17, 28, 15, 27, 16, 31, 16, 40, 10, 30, 20, 40, 12, 
23, 11, 26, 10, 36, 19, 37, 15, 34, 10, 43, 14, 26, 10, 26, 10, 
32, 10, 38, 17, 35, 10, 33, 11, 24, 10, 17, 15, 33, 12, 34, 30, 
18, 10, 30, 13, 27, 13, 28, 13, 23, 10, 34, 19, 28, 15, 32, 23, 
26, 25, 36, 20, 27, 11, 39, 15, 29, 10, 35, 10, 18, 10, 22, 13, 
30, 12, 23, 11, 24, 12, 22, 11, 28, 10, 24, 13, 29, 16, 31, 27
), group = c("Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative", 
"Positive", "Negative", "Positive", "Negative", "Positive", "Negative"
), prepost = structure(c(1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 
1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 
1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 
1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 
1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 
1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 
1L, 2L, 2L, 1L, 1L, 2L, 2L, 1L, 1L, 2L, 2L), levels = c("Before", 
"After"), class = "factor")), row.names = c(NA, -100L), class = "data.frame")

Thanks a lot for your time and attention !

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