gamma_poisson.R

library(manipulate)
manipulate({
  lambda <- seq(0, 5, length = 100)
  prior <- dgamma(lambda, a, b)
  post <- dgamma(lambda, a + sum(y), b + length(y))
  tibble(lambda, prior, post) %>%
    ggplot(aes(lambda, prior)) + geom_line() +
    geom_line(aes(y = post), color = "red") +
    ylab("density") +
    xlab(expression(lambda))
},
a = slider(1, 10, step = 1),
b = slider(1, 10, step = 1),
y = slider(1, 10, step = 1)
)