gganimate：结合transition_layers和geom_smooth

如何将geom_smooth(method = "lm) 函数与gganimate() 的transition_layers 结合起来，以便当各个条向上漂移/增长时，geom_smooth 的线性线出现，如下所示：geom_smooth 线所需外观的示例 https://user-images.githubusercontent.com/1775316/49728400-f0ba1b80-fc72-11e8-86c5-71ed84b247db.gif唯一的区别是，在我的例子中，当线条出现时，条形图会向上漂移，而不是点。

目前的条形效果很好，通过向上漂移而出现，这是通过使用 gganimate 的transition_layers 函数实现的。

但是，我不知道如何添加 geom_smooth 线，因此它会随着条形向上生长而出现。现在，该行出现在末尾，如下所示。

请参阅下文了解动画的当前外观。

这是我的问题的简单表示：

#Df for reprex
library(ggplot2)
library(tidyverse)

year <- as.numeric(c(1996:2002,
                     1996:2002,
                     1996:2002))
c <- c(39, 40, 67, 80, 30, 140, 90, 23, 100, 123,
       140, 1, 2, 1, 13, 3, 3, 30, 1, 3, 3)
df <- data.frame(year, c) %>%
  select(year, c) %>%
  arrange(year)

#Static plot
(static_plot <- ggplot(data = df) +
    geom_bar(data = df %>% filter(year == 1996), stat="identity", position ="stack",
             aes(x = year, y = c)) +
    geom_bar(data = df %>% filter(year == 1997), stat="identity", position ="stack",
             aes(x = year, y = c)) +
    geom_bar(data = df %>% filter(year == 1998), stat="identity", position ="stack",
             aes(x = year, y = c)) +
    geom_bar(data = df %>% filter(year == 1999), stat="identity", position ="stack",
             aes(x = year, y = c)) +
    geom_bar(data = df %>% filter(year == 2000), stat="identity", position ="stack",
             aes(x = year, y = c)) +
    geom_bar(data = df %>% filter(year == 2001), stat="identity", position ="stack",
             aes(x = year, y = c)) +
    geom_bar(data = df %>% filter(year == 2002), stat="identity", position ="stack",
             aes(x = year, y = c)) +
  labs(y = "year",
       x = "c",
       title = "Reprex") +
  geom_smooth(df, mapping = aes(x = year, y = c), method = "lm",
              colour = "black", se = F)
  )

#Animation
library(gganimate)
anim <- static_plot +
  transition_layers(layer_length = 1, transition_length = 1) +
  enter_drift(x_mod = 0, y_mod = -max(df$c))

animate(anim, fps = 10, duration = 10,
        width = 600, height = 500, renderer = gifski_renderer())

这是一种复制数据然后过滤数据的方法，以便每个版本逐渐显示更多年份。

library(dplyr); library(tidyr)

animate(
  df %>%
    count(year, wt = c, name = "c") %>%   # Aggregate for each year's total
    uncount(7, .id = "year_disp") %>%     # Make 7 copies, one for each year
    arrange(year_disp, year) %>% 
    mutate(year_disp = year_disp + min(df$year) - 1) %>%
    filter(year <= year_disp) %>%         # Only keep years up to "year_disp"
    ggplot(aes(year, c)) +
    geom_col(aes(group = year)) +   # "group" here connects each year to itself between frames
    geom_smooth(method = "lm", se = F) +
    transition_states(year_disp) +
    enter_drift(y_mod = -max(df$c)),
  fps = 10, duration = 10,
  width = 600, height = 500, renderer = gifski_renderer())