R/betaMCMC.R

In changxiulee/BayesianRasch: Bayesian Rasch Modeling

#' betaMCMC
#'
#' Extract the MCMC sample for the difficulty parameter of each category
#' @param obj An object from BPRM or BPRM.DIF.
#' @param g If it is a DIF model, specify the group in interest.

betaMCMC = function(obj, g = 1) {
  if(obj$DIF == TRUE){
    codaSamples = obj$mcmc[[g]]
  }else{
    codaSamples = obj$mcmc
  }
  data = obj$data
  item = obj$item

  betaMCMC.matrix = NULL
  codaSamples.matrix = as.matrix(codaSamples)
  item.variable = data[,item]
  if(min(apply(item.variable, 2, min,na.rm = TRUE)) == 0){item.variable = item.variable + 1}
  K = apply(item.variable, 2, max,na.rm = TRUE)
  p = ncol(item.variable)

  for(i in 1:p){
    betaMean = c()
    for(j in 1:nrow(codaSamples.matrix)){
      betaMean = c(betaMean, mean(codaSamples.matrix[j, paste0("beta[", i,",", 2:K[i],"]")]))
    }
    betaMCMC.matrix = cbind(betaMCMC.matrix, betaMean)
  }
  colnames(betaMCMC.matrix) = item
  betaMCMC.matrix
}