R/seq_scan_test.R

In smerc: Statistical Methods for Regional Counts

#' Sequential Scan Test
#'
#' Performs a series of sequential scan tests by ubpop. Only minimal information is returned
#' for each test. This is intended for internal use by the smerc package.
#'
#' @inheritParams optimal_ubpop
#'
#' @return Returns a list of \code{length(ubpop_seq)}. Each element of the
#' list has "pruned" set of results (as a list) for a scan test. Element of
#' the pruned list has the elements \code{tobs}, \code{zones}, \code{pvalue}.
#' @seealso \code{\link{scan.test}}
#' @author Joshua French
#' @export
#' @keywords internal
seq_scan_test <- function(coords, cases, pop,
                          ex = sum(cases) / sum(pop) * pop,
                          nsim = 499, alpha = 0.05,
                          ubpop_seq = seq(0.01, 0.5, len = 50),
                          longlat = FALSE, cl = NULL,
                          type = "poisson",
                          min.cases = 0,
                          simdist = "multinomial") {
  # argument checking
  type <- match.arg(type, c("poisson", "binomial"))
  simdist <- match.arg(simdist, c("multinomial", "poisson", "binomial"))
  arg_check_seq_scan_test(
    coords = coords, cases = cases,
    pop = pop, ex = ex, nsim = nsim,
    alpha = alpha, ubpop_seq = ubpop_seq,
    longlat = longlat,
    k = 1, w = diag(nrow(coords)),
    type = type, simdist = simdist,
    min.cases = min.cases
  )

  # convert to proper format
  coords <- as.matrix(coords)
  N <- nrow(coords)
  # compute inter-centroid distances
  d <- gedist(coords, longlat = longlat)

  # total number of cases
  ty <- sum(cases)
  # total population
  tpop <- sum(pop)

  # for each region, determine sorted nearest neighbors
  # subject to LARGEST population constraint
  nn <- scan.nn(d, pop, max(ubpop_seq))
  # logical vector of duplicate zones
  ldup <- nndup(nn, N)

  # compute number of cases in each candidate zone
  # only keep non-duplicated zones
  yin <- nn.cumsum(nn, cases)[!ldup]
  # compute number of cases in each candidate zone
  # only keep non-duplicated zones
  popin <- nn.cumsum(nn, pop)[!ldup]
  # determine non-duplicated zones
  zones <- nn2zones(nn)[!ldup]

  # compute test statistics for observed data
  if (type == "poisson") {
    ein <- nn.cumsum(nn, ex)[!ldup]
    eout <- sum(ex) - ein
    popout <- NULL
    tobs <- stat.poisson(yin, ty - yin, ein, eout)
  } else if (type == "binomial") {
    ein <- NULL
    eout <- NULL
    popout <- tpop - popin
    tobs <- stat.binom(yin, ty - yin, ty, popin, popout, tpop)
  }
  # set tobs to 0 when min.cases restriction not satisfied
  tobs[yin < min.cases] <- 0

  # compute logical vector specifying sequence of zones based
  # on ubpop constraints
  lseq_zones <- lapply(ubpop_seq, function(ubpop) {
    popin / tpop <= ubpop
  })

  # get sequence of tobs filtered by population constraints
  tobs_seq <- lapply(lseq_zones, function(lseq) {
    tobs[lseq]
  })

  # get sequence of candidate zones filtered by population constraints
  zones_seq <- lapply(lseq_zones, function(lseq) {
    zones[lseq]
  })

  # compute maximum test statistics for simulated data for all candidate zones
  # for each population constraint
  # each row contains the set of maximum statistics for each population constraint
  message("computing statistics for simulated data:")
  tsim_seq <- seq_scan_sim(
    nsim = nsim, nn = nn, ty = ty,
    ex = ex, type = type, ein = ein,
    eout = eout, popin = popin,
    popout = popout, tpop = tpop, cl = cl,
    simdist = simdist, pop = pop,
    min.cases = min.cases,
    ldup = ldup,
    lseq_zones = lseq_zones
  )

  message("computing p-values")
  pvalue_seq <- pbapply::pblapply(seq_along(ubpop_seq), function(i) {
    mc_pvalue_cpp(tobs = tobs_seq[[i]], tsim = tsim_seq[i, ])
  })

  # determine significant clusters for each population upper bound
  pruned_seq <- suppressWarnings(
    mapply(
      FUN = sig_noc,
      tobs = tobs_seq,
      zones = zones_seq,
      pvalue = pvalue_seq,
      MoreArgs = list(
        alpha = alpha,
        order_by = "tobs"
      ),
      SIMPLIFY = FALSE
    )
  )
  return(pruned_seq)
}
#' Argument checking for scan tests
#'
#' @param coords A matrix of coordinates
#' @param cases A vector of numeric cases
#' @param pop A vector of population values
#' @param ex A vector of expected counts
#' @param nsim A non-negative integer
#' @param alpha A value greater than 0
#' @param nreport Not used
#' @param ubpop_seq An strictly increasing sequence of values between min(pop)/sum(pop) and 1.
#' @param longlat A logical. TRUE is great circle distance.
#' @param parallel Not used.
#' @param k Number of nearest neighbors. Not always needed.
#' @param w A spatial proximity matrix
#' @param type Statistic type
#' @param simdist Distribution of simulation
#' @param min.cases Minimum number of cases. Only for scan.test.
#' @return NULL
#' @noRd
arg_check_seq_scan_test <- function(coords, cases, pop, ex, nsim, alpha,
                                    ubpop_seq, longlat, k, w, type, simdist,
                                    min.cases) {
  arg_check_scan_test(
    coords = coords, cases = cases,
    pop = pop, ex = ex, nsim = nsim,
    alpha = alpha, ubpop = 0.1,
    longlat = longlat,
    k = 1, w = diag(nrow(coords)),
    type = type, simdist = simdist,
    min.cases = min.cases
  )
  lb <- min(pop) / sum(pop)
  arg_check_ubpop_seq(ubpop_seq, lb)
}