R/methods-ivs2vas.R

In IntervalQuestionStat: Tools to Deal with Interval-Valued Responses in Questionnaires

## This file is part of the IntervalQuestionStat package for R

#' @title
#' Convert interval-valued responses into equivalent visual
#' analogue scale answers through mid-point criterion
#'
#' @description
#' This function allows to reduce each nonempty compact real interval collected
#' as a response in a questionnaire designed with interval-valued scales to its
#' mid-point so it can be considered as an answer from a visual analogue scale.
#' That is, given an nonempty compact real, interval, \eqn{A}, this method
#' returns its mid-point, which can be calculated as follows,
#' \deqn{\mathrm{mid}~A=\frac{\sup + \inf A}{2}.}
#'
#' @param x Either a single interval or either a list or matrix with several
#'          intervals stored as an \code{IntervalData} object or as an
#'          \code{IntervalList} or \code{IntervalMatrix} instance.
#'
#' @return 
#' This function returns the mid-points of the given interval-valued data to be
#' considered as visual analogue scale responses in a questionnaire stored
#' either as a \code{numeric} object if \code{x} argument is a single
#' interval or a list of intervals, that is, an \code{IntervalData} or
#' \code{IntervalList} instance, or either as a \code{data.frame} object whether
#' \code{x} is a matrix of intervals, that is, an \code{IntervalMatrix} object.
#'
#' @author José García-García \email{garciagarjose@@uniovi.es}
#'
#' @name ivs2vas
#' @rdname ivs2vas-methods
#' @docType methods
#' @aliases ivs2vas,IntervalData-method
#'          ivs2vas,IntervalList-method
#'          ivs2vas,IntervalMatrix-method
#'
#' @seealso
#' Interval-valued responses can be also associated to their corresponding
#' Likert-type scale's answer through the minimum \eqn{\theta}-distance
#' criterion implemented in the \code{\link{ivs2likert}()} function.
#' 
#' @export
#' 
#' @examples
#' ## Some ivs2vas() examples
#' 
#' ## A single interval-valued response
#' i <- IntervalData(3, 3.2)
#' ivs2vas(i)
#' 
#' ## A list of interval-valued responses
#' list <- IntervalList(c(3, 8.7), c(3.2, 9))
#' ivs2vas(list)
#' 
#' ## A matrix of interval-valued responses
#' matrix <- IntervalMatrix(matrix(c(1, 2.6, 1.5, 3, 3.8, 6, 4, 7), 2, 4))
#' ivs2vas(matrix)

setGeneric("ivs2vas",
           function(x) standardGeneric("ivs2vas"))

setMethod(f = "ivs2vas",
          signature(x = "IntervalData"),
          definition = function(x)
          {
            x@mid
          }
)

setMethod(f = "ivs2vas",
          signature(x = "IntervalList"),
          definition = function(x)
          {
            x@mid
          }
)

setMethod(f = "ivs2vas",
          signature(x = "IntervalMatrix"),
          definition = function(x)
          {
            output <- as.data.frame(x@mid)
            names(output) <- paste0("item", seq_len(ncol(x)))
            return(output)
          }
)