R/BRSM.transform.R

In changxiulee/BayesianRasch: Bayesian Rasch Modeling

#' BRSM.transform
#'
#' Transform BRSM parameter to make andrich threshold follow the sum-to-zero constraint
#'
#' @param mcmc MCMC sample from RSM model
#' @param item item involved in RSM model
#' @param K number of category

BRSM.transform = function(mcmc, item, K) {

  for(i in 1:nrow(mcmc)){
    ata = matrix(NA, length(item), K)
    for(j in 1:length(item)){
      for(k in 2:K){
        ata[j,k] = mcmc[i, paste0("beta[",j,"]")] + mcmc[i,paste0("thres[",k,"]")]
      }
    }
    #transform beta
    for(j in 1:length(item)){
      mcmc[i,paste0("beta[",j,"]")] = mean(ata[j,], na.rm = TRUE)
    }

    #transform thres
    for(k in 2:K){
      mcmc[i,paste0("thres[",k,"]")]  = ata[1, k] - mcmc[i,paste0("beta[",1,"]")]
    }
  }
  mcmc
}