ETS smoothing experiment

library(tidyverse)
library(fable)
library(gganimate)
set.seed(1)
df <- data.frame(x = 1:365,
                 y = cumsum(runif(365, min = -1)))

smoothy <- function(alpha1) {
  df %>%
    as_tsibble(index = x) %>%
    # using tip from @mitchoharawild
    # https://twitter.com/mitchoharawild/status/1220659030634434560
    model(ETS(y ~ trend(alpha = alpha1) + error("A") + season("N"))) %>%
    augment() %>%
    mutate(alpha = alpha1) %>%
    select(x, y, alpha, .fitted)
}

my_seq <- seq(from = 0.7, to = 0.15, length.out = 25*8)^3

animate(
  c(my_seq, rev(my_seq)) %>%
    map_dfr(smoothy, .id = "id") %>% 
    as_tibble() %>%
    mutate(id = as.numeric(id)) %>%
    ggplot(aes(x, .fitted, 
               group = id)) +
    geom_line(aes(y = y), color = "red") +
    geom_line(alpha = 1) +
    geom_text(data = . %>% group_by(id) %>% slice(1) %>%
                mutate(alpha_label = paste(
                  "Alpha:", scales::comma(alpha, accuracy = 0.0001))),
              x = 70, y = -7, size = 10, aes(label = alpha_label)) +
    annotate("segment", x = 0, xend = 225, y = -5, yend = -5) +
    geom_point(data = . %>% group_by(id) %>% slice(1),
               aes(x = alpha * 650), y = -5, 
               size = 3, shape = 21, fill = "gray92") +
    transition_manual(id), 
  fps = 25, duration = 16, type = "cairo", width = 500, height = 300)