Dirichlet regressioni coefficients - urlencode

Question

starting with this example of Dirichlet regression here.
My variable y is a vector of N = 3 elements and the Dirichlet regression model estimates N-1 coeff.
Let’s say I am interested in all 3 coefficients, how can I get them?
Thanks!
library(brms)
library(rstan)
library(dplyr)
bind <- function(...) cbind(...)
N <- 20
df <- data.frame(
y1 = rbinom(N, 10, 0.5), y2 = rbinom(N, 10, 0.7),
y3 = rbinom(N, 10, 0.9), x = rnorm(N)
) %>%
mutate(
size = y1 + y2 + y3,
y1 = y1 / size,
y2 = y2 / size,
y3 = y3 / size
)
df$y <- with(df, cbind(y1, y2, y3))
make_stancode(bind(y1, y2, y3) ~ x, df, dirichlet())
make_standata(bind(y1, y2, y3) ~ x, df, dirichlet())
fit <- brm(bind(y1, y2, y3) ~ x, df, dirichlet())
summary(fit)
Family: dirichlet
Links: muy2 = logit; muy3 = logit; phi = identity
Formula: bind(y1, y2, y3) ~ x
Data: df (Number of observations: 20)
Draws: 4 chains, each with iter = 2000; warmup = 1000; thin = 1;
total post-warmup draws = 4000
Population-Level Effects:
Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
muy2_Intercept 0.29 0.10 0.10 0.47 1.00 2830 2514
muy3_Intercept 0.56 0.09 0.38 0.73 1.00 2833 2623
muy2_x 0.04 0.11 -0.17 0.24 1.00 3265 2890
muy3_x -0.00 0.10 -0.20 0.19 1.00 3229 2973
Family Specific Parameters:
Estimate Est.Error l-95% CI u-95% CI Rhat Bulk_ESS Tail_ESS
phi 39.85 9.13 23.83 59.78 1.00 3358 2652
Draws were sampled using sampling(NUTS). For each parameter, Bulk_ESS
and Tail_ESS are effective sample size measures, and Rhat is the potential
scale reduction factor on split chains (at convergence, Rhat = 1).