Hi fellows

I am trying to use rstanarm for plotting posterior predictive distributions and related results. However I receive errors when i use functions such as “yrep = posterior_predict(stanfit, draws = 500)” . The error is:

```
Error in UseMethod("posterior_predict") :
no applicable method for 'posterior_predict' applied to an object of class "stanfit"
```

while I manually draw my posterior “f” value to a new variable like f_results then I use codes as follow:

```
'...
f_results = subset(draws2, variable="f") %>%
as_draws_df()
y=standata2$y
yrep=f_results[,1:174]
ppc_dens_overlay(y, yrep[1:50,])
```

I kept f_results[,1:174] and drop out the last three column which was related to chain numbers and other stuff. Also y is a one colomn with 174 rows. however when I use ppc_dens_overlay command then i got this error:

```
Error in validate_yrep(yrep, y) : is.matrix(yrep) is not TRUE
```

I guess there is something wrong with my yrep which is not defined as matrix by r. Otherwise all the dimensions are correct so why i cannot run it?

Could you kindly advice me for these two errors?