Re: [Bugs-r-devel] R2WinBUGS bug fix

[Uwe L. <li...@st...>]

I think this was proposed by Andrew Gelman in the original code and I 
already had the discussion but forgot the outcome (people would like to 
have it randomized?, Andrew?).

Anyway, a fix would be to add drop = FALSE as in

   sims <- sims [sample(n.sims), , drop = FALSE] # scramble (for 
convenience in analysis)

Best wishes,
Uwe



Dawn Woodard wrote:
> I found a bug in R2WinBUGS, which can be reproduced using the code below.  As
> a fix, I propose removing a single line of code in bugs.sims:
> 
>   sims <- sims [sample(n.sims),]    # scramble (for convenience in analysis)
> 
> This line of code scrambles the samples for each parameter.  What is the
> reason for doing this?  For some reason, when sims is a matrix with a single
> column (when the user has requested that only one parameter be returned) this
> line changes sims from a matrix object to a vector object.  
> 
> Thank you,
> Dawn
> 
> 
> 
> model.file <- function(){
> 	   for (j in 1:J){
>          y[j] ~ dnorm (theta[j], tau.y[j])
>          theta[j] ~ dnorm (mu.theta, tau.theta)
>          tau.y[j] <- pow(sigma.y[j], -2)
>        }
>        mu.theta ~ dnorm (0.0, 1.0E-6)
>        tau.theta <- pow(sigma.theta, -2)
>        sigma.theta ~ dunif (0, 1000)
> }
> 
> 
> # Some example data (see ?schools for details):
> data(schools)
> 
> J <- nrow(schools)
> y <- schools$estimate
> sigma.y <- schools$sd
> data <- list ("J", "y", "sigma.y")
> inits <- function(){
>     list(theta=rnorm(J, 0, 100), mu.theta=rnorm(1, 0, 100),
>          sigma.theta=runif(1, 0, 100))
> }
> ## or alternatively something like:
> # inits <- list(
> #   list(theta=rnorm(J, 0, 90), mu.theta=rnorm(1, 0, 90),
> #        sigma.theta=runif(1, 0, 90)),
> #   list(theta=rnorm(J, 0, 100), mu.theta=rnorm(1, 0, 100),
> #        sigma.theta=runif(1, 0, 100))
> #   list(theta=rnorm(J, 0, 110), mu.theta=rnorm(1, 0, 110),
> #        sigma.theta=runif(1, 0, 110)))
> 
> parameters <- c("mu.theta")
> 
> ## Not run: 
> ## You may need to edit "bugs.directory",
> ## also you need write access in the working directory:
> schools.sim <- bugs(data, inits, parameters, model.file,
>     n.chains=1, n.iter=5000,
>     bugs.directory="c:/Program Files/WinBUGS14/",
>     working.directory=NULL, clearWD=TRUE, DIC = F)
> print(schools.sim)
> 
> 
> 
> 
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