R/makeform.R

In bernardsilverman/modslavmse: Multiple Systems Estimates for estimating the prevalence of Modern Slavery

#' Construct a model formula for use by MCMCfit()
#'
#' Given the data frame \code{zdata} in \code{Rcapture} form, 
#'    creates a formula with the interactions given. 
#'
#' @details  
#' This routine is called by the Markov Chain Monte Carlo routine \code{\link{MCMCfit}}.  The routine \code{\link{MSEfit}} uses a formula with 
#'  numbered variables \eqn{c1, c2, \ldots } rather than using the names of the variables. 
#' 
#' @param zdata input data matrix
#' @param interactions a \eqn{2 \times m} matrix of two-factor interactions
#' @param includetwofac If \code{T} include all two factor \emph{excluding} those in \code{interactions}.  If \code{F} then include all main effects but only those two factor interactions in \code{interactions}
#' @export
makeform <- function(zdata, interactions = NULL, includetwofac = T) {
    # The matrix interactions is a 2 x m matrix If includetwofac=T then include all two
    # factor interactions but then exclude those in interactions If includetwofac=F then
    # include all main effects and then include those in interactions the value colch
    # will be used to include or exclude in the formula
    znames = dimnames(zdata)[[2]]
    nz = length(znames)
    varcount = znames[nz]
    varnames = znames[-nz]
    nv = nz - 1
    colch = "+"
    # first construct the full effects part of the formula
    form = paste(varnames, collapse = "+")
    if (includetwofac) {
        form = paste("(", form, ")^2", sep = "")
        colch = "-"
    }
    form = (paste(varcount, "~", form, sep = ""))
    # now modify if interactions is not null first create a matrix of names rather than
    # numbers
    if (!is.null(interactions)) {
        internames = varnames[interactions]
        dim(internames) = dim(as.matrix(interactions))
        intervec = apply(internames, 2, paste, collapse = ":")
        form = paste(form, paste(intervec, collapse = colch), sep = colch)
    }
    return(form)
    
}