jags.parallel - Error in get(name, envir = envir) : invalid first argument

Question

When using jags.parallel, I get the following error:

> out <- jags.parallel(win.data, inits, params, "Poisson.OD.t.test.txt",
+ nc, ni, nb, nt);
Error in get(name, envir = envir) : invalid first argument

The same call using jags function runs OK. I have only found one thread on this topic, but there is only one speculative suggestion that does not apply nor work here.

Reproducible code, taken from Introduction to WinBUGS for ecologists, see chapter 14.1 (slightly modified):

set.seed(123)

### 14.1.2. Data generation
n.site <- 10
x <- gl(n = 2, k = n.site, labels = c("grassland", "arable"))
eps <- rnorm(2*n.site, mean = 0, sd = 0.5)# Normal random effect
lambda.OD <- exp(0.69 +(0.92*(as.numeric(x)-1) + eps) )
lambda.Poisson <- exp(0.69 +(0.92*(as.numeric(x)-1)) ) # For comparison

C.OD <- rpois(n = 2*n.site, lambda = lambda.OD)
C.Poisson <- rpois(n = 2*n.site, lambda = lambda.Poisson)

### 14.1.4. Analysis using WinBUGS
# Define model
sink("Poisson.OD.t.test.txt")
cat("
model {
# Priors
 alpha ~ dnorm(0,0.001)
 beta ~ dnorm(0,0.001)
 sigma ~ dunif(0, 10)   
 tau <- 1 / (sigma * sigma)
 maybe_overdisp <- mean(exp_eps[])

# Likelihood
 for (i in 1:n) {
    C.OD[i] ~ dpois(lambda[i]) 
    log(lambda[i]) <- alpha + beta *x[i] #+ eps[i]
    eps[i] ~ dnorm(0, tau)
    exp_eps[i] <- exp(eps[i])
 }
}
",fill=TRUE)
sink()


# Bundle data
win.data <- list(C.OD = C.OD, x = as.numeric(x)-1, n = length(x))

# Inits function
inits <- function(){ list(alpha=rlnorm(1), beta=rlnorm(1), sigma = rlnorm(1))}

# Parameters to estimate
params <- c("lambda","alpha", "beta", "sigma", "maybe_overdisp")

# MCMC settings
nc <- 3     # Number of chains
ni <- 3000     # Number of draws from posterior per chain
nb <- 1000     # Number of draws to discard as burn-in
nt <- 5     # Thinning rate

require(R2jags)

# THIS WORKS FINE
out <- R2jags::jags(win.data, inits, params, "Poisson.OD.t.test.txt",
    nc, ni, nb, nt);

# THIS PRODUCES ERROR
out <- jags.parallel(win.data, inits, params, "Poisson.OD.t.test.txt",
    nc, ni, nb, nt);

# THIS ALSO PRODUCES ERROR
out <- do.call(jags.parallel, list(win.data, inits, params, "Poisson.OD.t.test.txt",
    nc, ni, nb, nt));

Answer 1

Jags/R had practically two problems with this line:

out <- jags.parallel(win.data, inits, params, "Poisson.OD.t.test.txt",
    nc, ni, nb, nt);

Both are related to evaluation of function parameters - he is probably not able to resolve parameters which refer to other R variables:

1) The win.data was encoded as variable names as usually for WinBUGS/Jags:

win.data <- list(C.OD = C.OD, x = as.numeric(x)-1, n = length(x))`

but jags.parallel issues the error "Error in get(name, envir = envir) : invalid first argument". He wants the data in this format:

windata <- list("C.OD", "x", "n")

Why? Don't ask me... I discovered this when reading the example of ?jags.

2) The arguments nc, ni, nb, nt in function call are a problem! If I put constants, it is OK, but references to variables are unacceptable for him. Don't ask me why. Remedy found at strange jags.parallel error / avoiding lazy evaluation in function call.

The complete fix looks like:

out <- do.call(jags.parallel, list(names(win.data), inits, params, "Poisson.OD.t.test.txt",
    nc, ni, nb, nt));

Answer 2

sometimes this error occurs when you use a vectorized function inside parlapply. I've solved the problem by adding "do.call" and "mapply" functions to cluster.export