R: Extract Prior Draws

prior_draws.brmsfit {brms} | R Documentation

## Extract Prior Draws

### Description

Extract prior draws of specified parameters

### Usage

    ## S3 method for class 'brmsfit'
    prior_draws(x, variable = NULL, pars = NULL, ...)

    prior_draws(x, ...)

    prior_samples(x, ...)

### Arguments

`x` | An `R` object typically of class `brmsfit`.
`variable` | A character vector providing the variables to extract. By default, all variables are extracted.
`pars` | Deprecated alias of `variable`. For reasons of backwards compatibility, `pars` is interpreted as a vector of regular expressions by default unless `fixed = TRUE` is specified.
`...` | Arguments passed to individual methods (if applicable).

### Details

To make use of this function, the model must contain draws of prior distributions. This can be ensured by setting `sample_prior = TRUE` in function `brm`. Priors of certain parameters cannot be saved for technical reasons. For instance, this is the case for the population-level intercept, which is only computed after fitting the model by default. If you want to treat the intercept as part of all the other regression coefficients, so that sampling from its prior becomes possible, use `... ~ 0 + Intercept + ...` in the formulas.

### Value

A `data.frame` containing the prior draws.

### Examples

    ## Not run:
    fit <- brm(rating ~ treat + period + carry + (1|subject),
               data = inhaler, family = "cumulative",
               prior = set_prior("normal(0,2)", class = "b"),
               sample_prior = TRUE)

    # extract all prior draws
    draws1 <- prior_draws(fit)
    head(draws1)

    # extract prior draws for the coefficient of 'treat'
    draws2 <- prior_draws(fit, "b_treat")
    head(draws2)

    ## End(Not run)

[Package brms version 2.16.3 Index]