I am trying to calculate rhats for posterior predictions from a model fit using `brms`

. Based on this old thread, I am trying to do this using `tidybayes`

.

As a MWE, we can use the data/model in the `tidy-brms`

vignette:

```
set.seed(5)
n = 10
n_condition = 5
ABC =
tibble(
condition = rep(c("A","B","C","D","E"), n),
response = rnorm(n * 5, c(0,1,2,1,-1), 0.5)
)
m = brm(
response ~ (1|condition),
data = ABC,
prior = c(
prior(normal(0, 1), class = Intercept),
prior(student_t(3, 0, 1), class = sd),
prior(student_t(3, 0, 1), class = sigma)
),
control = list(adapt_delta = .99)
)
```

If I call `spread_draws()`

on the resulting model, it returns a tibble that has the chain information stored as `.chains`

:

```
> m %>%
+ spread_draws(r_condition[condition, term]) %>%
+ head()
# A tibble: 6 × 6
# Groups: condition, term [1]
condition term r_condition .chain .iteration .draw
<chr> <chr> <dbl> <int> <int> <int>
1 A Intercept 0.683 1 1 1
2 A Intercept -0.779 1 2 2
3 A Intercept -0.580 1 3 3
4 A Intercept -0.717 1 4 4
5 A Intercept -0.786 1 5 5
6 A Intercept -0.818 1 6 6
```

However, if I call `add_epred_draws()`

, the `.chains`

information is all missing:

```
> ABC %>%
+ modelr::data_grid(condition) %>%
+ add_epred_draws(m) %>%
+ head()
# A tibble: 6 × 6
# Groups: condition, .row [1]
condition .row .chain .iteration .draw .epred
<chr> <int> <int> <int> <int> <dbl>
1 A 1 NA NA 1 0.406
2 A 1 NA NA 2 0.114
3 A 1 NA NA 3 0.361
4 A 1 NA NA 4 0.282
5 A 1 NA NA 5 0.253
6 A 1 NA NA 6 0.596
```

Why is it missing? I need the `.chains`

info to get the rhats.