stat_function not transitioning over transition_states - r

Question

I'm trying to write my own Central Limit Theorem demonstration using ggplot2 and am unable to get my stat_function to display a changing normal distribution.
below is my code, I want the normal distribution in stat_function to transition through different states; specifically, I'm hoping for it to change the standard deviation to correspond with each value in dataset. Any help would be greatly appreciated.
#library defs
library(gganimate)
library(ggplot2)
library(transformr)
#initialization for distribution, rolls, and vectors
k = 2
meanr = 1/k
sdr = 1/k
br = sdr/10
rolls <- 200
avg <- 1
dataset <- 1
s <- 1
#loop through to create vectors of sample statistics from 200 samples of size i
#avg is sample average, s is standard deviations of sample means, and dataset is the indexes to run the transition states
for (i in c(1:40)){
for (j in 1:rolls){
avg <- c(avg,mean(rexp(i,k)))
}
dataset <- c(dataset, rep(i,rolls))
s <- c(s,rep(sdr/sqrt(i),rolls))
}
#remove initialized vector information as it was only created to start loops
avg <- avg[-1]
rn <- rn[-1]
dataset <- dataset[-1]
s <- s[-1]
#dataframe
a <- data.frame(avgf=avg, rnf = rn,datasetf = dataset,sf = s)
#plot histogram, density function, and normal distribution
ggplot(a,aes(x=avg,y=s))+
geom_histogram(aes(y = ..density..), binwidth = br,fill='beige',col='black')+
geom_line(aes(y = ..density..,colour = 'Empirical'),lwd=2, stat = 'density') +
stat_function(fun = dnorm, aes(colour = 'Normal', y = s),lwd=2,args=list(mean=meanr,sd = mean(s)))+
scale_y_continuous(labels = scales::percent_format()) +
scale_color_discrete(name = "Densities", labels = c("Empirical", "Normal"))+
labs(x = 'Sample Average',title = 'Sample Size: {closest_state}')+
transition_states(dataset,4,4)+ view_follow(fixed_x = TRUE)

Answer 1

I think it's difficult to use stat_function here because the dnorm function that you are passing includes a grouped variable (mean(s)). There is no way to indicate that you wish to group s by the dataset column, and the transition_states function doesn't filter the whole data frame. You could use transition_filter to filter the whole data frame, but this would be laborious.
It's not much work to just add a dnorm to your input data frame and plot it as a line, particularly since the rest of your code can be simplified substantially. Here's a fully reproducible example:
library(gganimate)
library(ggplot2)
library(transformr)
k <- 2
meanr <- sdr <- 1/k
br <- sdr/10
rolls <- 200
a <- do.call(rbind, lapply(1:40, function(i){
data.frame(avg = replicate(rolls, mean(rexp(i, k))),
dataset = rep(i, rolls),
x = seq(0, 2, length.out = rolls),
s = dnorm(seq(0, 2, length.out = rolls),
meanr, sdr/sqrt(i))) }))
ggplot(a, aes(x = avg, group = dataset)) +
geom_histogram(aes(y = ..density..), fill = 'beige',
colour = "black", binwidth = br) +
geom_line(aes(y = ..density.., colour = 'Empirical'),
lwd = 2, stat = 'density', alpha = 0.5) +
geom_line(aes(x = x, y = s, colour = "Normal"), size = 2, alpha = 0.5) +
scale_y_continuous(labels = scales::percent_format()) +
coord_cartesian(xlim = c(0, 2)) +
scale_color_discrete(name = "Densities", labels = c("Empirical", "Normal")) +
labs(x = 'Sample Average', title = 'Sample Size: {closest_state}') +
transition_states(dataset, 4, 4) +
view_follow(fixed_x = TRUE, fixed_y = TRUE)