R/Utils.R

In mstDIF: A Collection of DIF Tests for Multistage Tests

extract_it_pars <- function(AllModelClass){
  itemnames <- mirt::extract.mirt(AllModelClass, "itemnames")
  pars <- mirt::coef(AllModelClass, IRTpars = TRUE, as.data.frame = TRUE)
  if(!is.data.frame(pars)) {
    warning("Only the item parameters based on the first group are used for the DIF test.", call. = FALSE)
    pars <- pars[[1]]
  }
  get_it_pars(pars)
}

get_it_pars <- function(pars){
  row_names <- rownames(pars)
  data.frame(a = pars[grep(".a", row_names, fixed = TRUE), ],
             b = pars[grep(".b", row_names, fixed = TRUE), ],
             g = pars[grep(".g", row_names, fixed = TRUE), ],
             u = pars[grep(".u", row_names, fixed = TRUE), ],
             row.names = sub(".a", "",
                             grep(".a", row_names,
                                  fixed = TRUE, value = TRUE),
                             fixed = TRUE))
}

# a function that removes the unused arguments from a call
clean_call <- function(call, warning = TRUE) {

  # get the function
  fun <- call[[1]]

  names_call <- names(call)
  which_unused <- which(!names_call %in% names(formals(eval(fun))))

  # warning message:
  if(length(which_unused[-1]) == 0){
    return(call)
  } else {
    if(warning)
      warning("The following objects are ignored by ", fun, ": \n",
              paste(names_call[which_unused][-1],
                    call[which_unused][-1], sep = " = ", collapse = "\n"),
              call. = FALSE, immediate. = TRUE)

    # evaluate function
    return(call[-which_unused[-1]])
  }
}