sigma_tween.R

library(tweenr)
library(gganimate)
library(ggplot2)
library(tidyverse)

#' define the 4 states
state1 <- data_frame(mean = 0, 
                     sd = 1)
state2 <- data_frame(mean = 0, 
                     sd = 3)
state3 <- data_frame(mean = 0, 
                     sd = 0.5)
state4 <- data_frame(mean = 0, 
                     sd = 1)

#' tweening the parameters
param_list <- list(state1, state2, state3, state4)
param_tween <- tween_states(param_list, tweenlength = 10, statelength = 2, ease = "cubic-in-out", nframe = 200)

#' function to generate the densituy distributions
make_dist <- function(df){
  out <- data_frame(x = seq(-8, 9, length = 200),
                    y = dnorm(x, mean = df$mean, sd = df$sd),
                    mean = df$mean,
                    sd = df$sd)
  return(out)
}

#' generating the tweened distributiobs
dist_tween <- param_tween %>%
                group_by(.frame)%>%
                summarize(mean = mean(mean),
                          sd = mean(sd)) %>%
                group_by(.frame)%>%
                nest() %>%
                mutate(dist = map(data, make_dist))%>%
                unnest(dist)

#' making the labels
dist_tween %>%
  group_by(.frame)%>%
  summarise(mean = max(mean),
            sd = max(sd)) %>%
  mutate(mulab = paste0("mu==", round(mean, digits = 2)),
         siglab = paste0("sigma==", round(sd, digits = 2)))->label_states

#' the animation plot
sigma_anim <- dist_tween %>%
  ggplot(aes(x, y)) + 
    geom_ribbon(aes(frame = .frame, ymin = 0, ymax = y),color = "#2171b5", size = 3, fill = "#bdd7e7") +
    #geom_point(aes(frame  = .frame))+
    geom_text(data = label_states, aes(label = mulab, x=mean, y = .1, frame = .frame), parse = T)+
    geom_text(data = label_states, aes(label = siglab, x=mean, y = 0.05, frame = .frame), parse = T)+
    theme_minimal()

# Set up options and animate
animation::ani.options(interval = 1/30, ani.width = 800/1.5, ani.height = 500/1.5)
gganimate(sigma_anim, filename = "sigma_anim2.gif", title_frame = F)