Stan Development Team

CmdStanR: the R interface to CmdStan.

Details

CmdStanR (cmdstanr package) is an interface to Stan (mc-stan.org) for R users. It provides the necessary objects and functions to compile a Stan program and run Stan's algorithms from R via CmdStan, the shell interface to Stan (mc-stan.org/users/interfaces/cmdstan).

Different ways of interfacing with Stan’s C++

The RStan interface (rstan package) is an in-memory interface to Stan and relies on R packages like Rcpp and inline to call C++ code from R. On the other hand, the CmdStanR interface does not directly call any C++ code from R, instead relying on the CmdStan interface behind the scenes for compilation, running algorithms, and writing results to output files.

Advantages of RStan

Advantages of CmdStanR

  • Compatible with latest versions of Stan. Keeping up with Stan releases is complicated for RStan, often requiring non-trivial changes to the rstan package and new CRAN releases of both rstan and StanHeaders. With CmdStanR the latest improvements in Stan will be available from R immediately after updating CmdStan using cmdstanr::install_cmdstan().

  • Fewer installation issues (e.g., no need to mess with Makevars files).

  • Running Stan via external processes results in fewer unexpected crashes, especially in RStudio.

  • Less memory overhead.

  • More permissive license. RStan uses the GPL-3 license while the license for CmdStanR is BSD-3, which is a bit more permissive and is the same license used for CmdStan and the Stan C++ source code.

Getting started

CmdStanR requires a working version of CmdStan. If you already have CmdStan installed see cmdstan_model() to get started, otherwise see install_cmdstan() to install CmdStan. The vignette Getting started with CmdStanR demonstrates the basic functionality of the package.

See also

The CmdStanR website (mc-stan.org/cmdstanr) for online documentation and tutorials.

The Stan and CmdStan documentation:

Examples

# \dontrun{
library(cmdstanr)
library(posterior)
library(bayesplot)
color_scheme_set("brightblue")

# Set path to CmdStan
# (Note: if you installed CmdStan via install_cmdstan() with default settings
# then setting the path is unnecessary but the default below should still work.
# Otherwise use the `path` argument to specify the location of your
# CmdStan installation.)
set_cmdstan_path(path = NULL)
#> CmdStan path set to: /Users/jgabry/.cmdstan/cmdstan-2.32.2

# Create a CmdStanModel object from a Stan program,
# here using the example model that comes with CmdStan
file <- file.path(cmdstan_path(), "examples/bernoulli/bernoulli.stan")
mod <- cmdstan_model(file)
mod$print()
#> data {
#>   int<lower=0> N;
#>   array[N] int<lower=0,upper=1> y;
#> }
#> parameters {
#>   real<lower=0,upper=1> theta;
#> }
#> model {
#>   theta ~ beta(1,1);  // uniform prior on interval 0,1
#>   y ~ bernoulli(theta);
#> }

# Data as a named list (like RStan)
stan_data <- list(N = 10, y = c(0,1,0,0,0,0,0,0,0,1))

# Run MCMC using the 'sample' method
fit_mcmc <- mod$sample(
  data = stan_data,
  seed = 123,
  chains = 2,
  parallel_chains = 2
)
#> Running MCMC with 2 parallel chains...
#> 
#> Chain 1 Iteration:    1 / 2000 [  0%]  (Warmup) 
#> Chain 1 Iteration:  100 / 2000 [  5%]  (Warmup) 
#> Chain 1 Iteration:  200 / 2000 [ 10%]  (Warmup) 
#> Chain 1 Iteration:  300 / 2000 [ 15%]  (Warmup) 
#> Chain 1 Iteration:  400 / 2000 [ 20%]  (Warmup) 
#> Chain 1 Iteration:  500 / 2000 [ 25%]  (Warmup) 
#> Chain 1 Iteration:  600 / 2000 [ 30%]  (Warmup) 
#> Chain 1 Iteration:  700 / 2000 [ 35%]  (Warmup) 
#> Chain 1 Iteration:  800 / 2000 [ 40%]  (Warmup) 
#> Chain 1 Iteration:  900 / 2000 [ 45%]  (Warmup) 
#> Chain 1 Iteration: 1000 / 2000 [ 50%]  (Warmup) 
#> Chain 1 Iteration: 1001 / 2000 [ 50%]  (Sampling) 
#> Chain 1 Iteration: 1100 / 2000 [ 55%]  (Sampling) 
#> Chain 1 Iteration: 1200 / 2000 [ 60%]  (Sampling) 
#> Chain 1 Iteration: 1300 / 2000 [ 65%]  (Sampling) 
#> Chain 1 Iteration: 1400 / 2000 [ 70%]  (Sampling) 
#> Chain 1 Iteration: 1500 / 2000 [ 75%]  (Sampling) 
#> Chain 1 Iteration: 1600 / 2000 [ 80%]  (Sampling) 
#> Chain 1 Iteration: 1700 / 2000 [ 85%]  (Sampling) 
#> Chain 1 Iteration: 1800 / 2000 [ 90%]  (Sampling) 
#> Chain 1 Iteration: 1900 / 2000 [ 95%]  (Sampling) 
#> Chain 1 Iteration: 2000 / 2000 [100%]  (Sampling) 
#> Chain 2 Iteration:    1 / 2000 [  0%]  (Warmup) 
#> Chain 2 Iteration:  100 / 2000 [  5%]  (Warmup) 
#> Chain 2 Iteration:  200 / 2000 [ 10%]  (Warmup) 
#> Chain 2 Iteration:  300 / 2000 [ 15%]  (Warmup) 
#> Chain 2 Iteration:  400 / 2000 [ 20%]  (Warmup) 
#> Chain 2 Iteration:  500 / 2000 [ 25%]  (Warmup) 
#> Chain 2 Iteration:  600 / 2000 [ 30%]  (Warmup) 
#> Chain 2 Iteration:  700 / 2000 [ 35%]  (Warmup) 
#> Chain 2 Iteration:  800 / 2000 [ 40%]  (Warmup) 
#> Chain 2 Iteration:  900 / 2000 [ 45%]  (Warmup) 
#> Chain 2 Iteration: 1000 / 2000 [ 50%]  (Warmup) 
#> Chain 2 Iteration: 1001 / 2000 [ 50%]  (Sampling) 
#> Chain 2 Iteration: 1100 / 2000 [ 55%]  (Sampling) 
#> Chain 2 Iteration: 1200 / 2000 [ 60%]  (Sampling) 
#> Chain 2 Iteration: 1300 / 2000 [ 65%]  (Sampling) 
#> Chain 2 Iteration: 1400 / 2000 [ 70%]  (Sampling) 
#> Chain 2 Iteration: 1500 / 2000 [ 75%]  (Sampling) 
#> Chain 2 Iteration: 1600 / 2000 [ 80%]  (Sampling) 
#> Chain 2 Iteration: 1700 / 2000 [ 85%]  (Sampling) 
#> Chain 2 Iteration: 1800 / 2000 [ 90%]  (Sampling) 
#> Chain 2 Iteration: 1900 / 2000 [ 95%]  (Sampling) 
#> Chain 2 Iteration: 2000 / 2000 [100%]  (Sampling) 
#> Chain 1 finished in 0.0 seconds.
#> Chain 2 finished in 0.0 seconds.
#> 
#> Both chains finished successfully.
#> Mean chain execution time: 0.0 seconds.
#> Total execution time: 0.2 seconds.
#> 

# Use 'posterior' package for summaries
fit_mcmc$summary()
#> # A tibble: 2 × 10
#>   variable   mean median    sd   mad      q5    q95  rhat ess_bulk ess_tail
#>   <chr>     <num>  <num> <num> <num>   <num>  <num> <num>    <num>    <num>
#> 1 lp__     -7.30  -7.03  0.721 0.380 -8.82   -6.75   1.00     902.    1006.
#> 2 theta     0.247  0.233 0.122 0.129  0.0786  0.470  1.00     762.     712.

# Get posterior draws
draws <- fit_mcmc$draws()
print(draws)
#> # A draws_array: 1000 iterations, 2 chains, and 2 variables
#> , , variable = lp__
#> 
#>          chain
#> iteration    1    2
#>         1 -6.8 -6.8
#>         2 -6.9 -6.8
#>         3 -7.0 -7.0
#>         4 -6.9 -7.1
#>         5 -6.7 -7.0
#> 
#> , , variable = theta
#> 
#>          chain
#> iteration    1    2
#>         1 0.28 0.21
#>         2 0.19 0.20
#>         3 0.16 0.17
#>         4 0.20 0.36
#>         5 0.25 0.34
#> 
#> # ... with 995 more iterations

# Convert to data frame using posterior::as_draws_df
as_draws_df(draws)
#> # A draws_df: 1000 iterations, 2 chains, and 2 variables
#>    lp__ theta
#> 1  -6.8  0.28
#> 2  -6.9  0.19
#> 3  -7.0  0.16
#> 4  -6.9  0.20
#> 5  -6.7  0.25
#> 6  -7.1  0.36
#> 7  -9.0  0.55
#> 8  -7.2  0.15
#> 9  -6.8  0.23
#> 10 -7.5  0.42
#> # ... with 1990 more draws
#> # ... hidden reserved variables {'.chain', '.iteration', '.draw'}

# Plot posterior using bayesplot (ggplot2)
mcmc_hist(fit_mcmc$draws("theta"))
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.


# Call CmdStan's diagnose and stansummary utilities
fit_mcmc$cmdstan_diagnose()
#> Processing csv files: /var/folders/s0/zfzm55px2nd2v__zlw5xfj2h0000gn/T/RtmpFBtN6X/bernoulli-202307251435-1-2078cc.csv, /var/folders/s0/zfzm55px2nd2v__zlw5xfj2h0000gn/T/RtmpFBtN6X/bernoulli-202307251435-2-2078cc.csv
#> 
#> Checking sampler transitions treedepth.
#> Treedepth satisfactory for all transitions.
#> 
#> Checking sampler transitions for divergences.
#> No divergent transitions found.
#> 
#> Checking E-BFMI - sampler transitions HMC potential energy.
#> E-BFMI satisfactory.
#> 
#> Effective sample size satisfactory.
#> 
#> Split R-hat values satisfactory all parameters.
#> 
#> Processing complete, no problems detected.
fit_mcmc$cmdstan_summary()
#> Inference for Stan model: bernoulli_model
#> 2 chains: each with iter=(1000,1000); warmup=(0,0); thin=(1,1); 2000 iterations saved.
#> 
#> Warmup took (0.0040, 0.0030) seconds, 0.0070 seconds total
#> Sampling took (0.011, 0.011) seconds, 0.022 seconds total
#> 
#>                 Mean     MCSE  StdDev     5%   50%   95%  N_Eff  N_Eff/s    R_hat
#> 
#> lp__            -7.3  2.6e-02    0.72   -8.8  -7.0  -6.8    781    35502      1.0
#> accept_stat__   0.92  8.3e-03    0.13   0.64  0.97   1.0    235    10662  1.0e+00
#> stepsize__      0.95  7.9e-02   0.079   0.87   1.0   1.0    1.0       46  2.0e+13
#> treedepth__      1.4  1.1e-02    0.48    1.0   1.0   2.0   1874    85179  1.0e+00
#> n_leapfrog__     2.5  1.4e-01     1.3    1.0   3.0   3.0     89     4050  1.0e+00
#> divergent__     0.00      nan    0.00   0.00  0.00  0.00    nan      nan      nan
#> energy__         7.8  3.6e-02    1.00    6.8   7.5   9.6    775    35215  1.0e+00
#> 
#> theta           0.25  4.3e-03    0.12  0.079  0.23  0.47    796    36197      1.0
#> 
#> Samples were drawn using hmc with nuts.
#> For each parameter, N_Eff is a crude measure of effective sample size,
#> and R_hat is the potential scale reduction factor on split chains (at 
#> convergence, R_hat=1).

# For models fit using MCMC, if you like working with RStan's stanfit objects
# then you can create one with rstan::read_stan_csv()

# stanfit <- rstan::read_stan_csv(fit_mcmc$output_files())


# Run 'optimize' method to get a point estimate (default is Stan's LBFGS algorithm)
# and also demonstrate specifying data as a path to a file instead of a list
my_data_file <- file.path(cmdstan_path(), "examples/bernoulli/bernoulli.data.json")
fit_optim <- mod$optimize(data = my_data_file, seed = 123)
#> Initial log joint probability = -9.51104 
#>     Iter      log prob        ||dx||      ||grad||       alpha      alpha0  # evals  Notes  
#>        6      -5.00402   0.000103557   2.55661e-07           1           1        9    
#> Optimization terminated normally:  
#>   Convergence detected: relative gradient magnitude is below tolerance 
#> Finished in  0.1 seconds.

fit_optim$summary()
#> # A tibble: 2 × 2
#>   variable estimate
#>   <chr>       <num>
#> 1 lp__        -5.00
#> 2 theta        0.2 


# Run 'variational' method to approximate the posterior (default is meanfield ADVI)
fit_vb <- mod$variational(data = stan_data, seed = 123)
#> ------------------------------------------------------------ 
#> EXPERIMENTAL ALGORITHM: 
#>   This procedure has not been thoroughly tested and may be unstable 
#>   or buggy. The interface is subject to change. 
#> ------------------------------------------------------------ 
#> Gradient evaluation took 6e-06 seconds 
#> 1000 transitions using 10 leapfrog steps per transition would take 0.06 seconds. 
#> Adjust your expectations accordingly! 
#> Begin eta adaptation. 
#> Iteration:   1 / 250 [  0%]  (Adaptation) 
#> Iteration:  50 / 250 [ 20%]  (Adaptation) 
#> Iteration: 100 / 250 [ 40%]  (Adaptation) 
#> Iteration: 150 / 250 [ 60%]  (Adaptation) 
#> Iteration: 200 / 250 [ 80%]  (Adaptation) 
#> Success! Found best value [eta = 1] earlier than expected. 
#> Begin stochastic gradient ascent. 
#>   iter             ELBO   delta_ELBO_mean   delta_ELBO_med   notes  
#>    100           -6.262             1.000            1.000 
#>    200           -6.263             0.500            1.000 
#>    300           -6.307             0.336            0.007   MEDIAN ELBO CONVERGED 
#> Drawing a sample of size 1000 from the approximate posterior...  
#> COMPLETED. 
#> Finished in  0.1 seconds.

fit_vb$summary()
#> # A tibble: 3 × 7
#>   variable      mean median    sd   mad     q5      q95
#>   <chr>        <num>  <num> <num> <num>  <num>    <num>
#> 1 lp__        -7.18  -6.94  0.588 0.259 -8.36  -6.75   
#> 2 lp_approx__ -0.515 -0.221 0.692 0.303 -2.06  -0.00257
#> 3 theta        0.263  0.246 0.115 0.113  0.106  0.481  

# Plot approximate posterior using bayesplot
mcmc_hist(fit_vb$draws("theta"))
#> `stat_bin()` using `bins = 30`. Pick better value with `binwidth`.



# Specifying initial values as a function
fit_mcmc_w_init_fun <- mod$sample(
  data = stan_data,
  seed = 123,
  chains = 2,
  refresh = 0,
  init = function() list(theta = runif(1))
)
#> Running MCMC with 2 sequential chains...
#> 
#> Chain 1 finished in 0.0 seconds.
#> Chain 2 finished in 0.0 seconds.
#> 
#> Both chains finished successfully.
#> Mean chain execution time: 0.0 seconds.
#> Total execution time: 0.3 seconds.
#> 
fit_mcmc_w_init_fun_2 <- mod$sample(
  data = stan_data,
  seed = 123,
  chains = 2,
  refresh = 0,
  init = function(chain_id) {
    # silly but demonstrates optional use of chain_id
    list(theta = 1 / (chain_id + 1))
  }
)
#> Running MCMC with 2 sequential chains...
#> 
#> Chain 1 finished in 0.0 seconds.
#> Chain 2 finished in 0.0 seconds.
#> 
#> Both chains finished successfully.
#> Mean chain execution time: 0.0 seconds.
#> Total execution time: 0.3 seconds.
#> 
fit_mcmc_w_init_fun_2$init()
#> [[1]]
#> [[1]]$theta
#> [1] 0.5
#> 
#> 
#> [[2]]
#> [[2]]$theta
#> [1] 0.3333333
#> 
#> 

# Specifying initial values as a list of lists
fit_mcmc_w_init_list <- mod$sample(
  data = stan_data,
  seed = 123,
  chains = 2,
  refresh = 0,
  init = list(
    list(theta = 0.75), # chain 1
    list(theta = 0.25)  # chain 2
  )
)
#> Running MCMC with 2 sequential chains...
#> 
#> Chain 1 finished in 0.0 seconds.
#> Chain 2 finished in 0.0 seconds.
#> 
#> Both chains finished successfully.
#> Mean chain execution time: 0.0 seconds.
#> Total execution time: 0.4 seconds.
#> 
fit_optim_w_init_list <- mod$optimize(
  data = stan_data,
  seed = 123,
  init = list(
    list(theta = 0.75)
  )
)
#> Initial log joint probability = -11.6657 
#>     Iter      log prob        ||dx||      ||grad||       alpha      alpha0  # evals  Notes  
#>        6      -5.00402   0.000237915   9.55309e-07           1           1        9    
#> Optimization terminated normally:  
#>   Convergence detected: relative gradient magnitude is below tolerance 
#> Finished in  0.1 seconds.
fit_optim_w_init_list$init()
#> [[1]]
#> [[1]]$theta
#> [1] 0.75
#> 
#> 
# }