Create separate function to calc popsize and sampsize

[smishr]

In R survey there is an inner function called as.fpc which returns popsize and sampsize for any arbitrary design given strata and cluster arguments. It should be a long term goal to achieve similar in Survey.jl

function (df, strata, ids, pps = FALSE) 
{
  count <- function(x) sum(!duplicated(x))
  sampsize <- matrix(ncol = ncol(ids), nrow = nrow(ids))
  for (i in 1:ncol(ids)) split(sampsize[, i], strata[, i]) <- lapply(split(ids[, 
    i], strata[, i]), count)
  if (is.null(df)) {
    rval <- list(popsize = NULL, sampsize = sampsize)
    class(rval) = "survey_fpc"
    return(rval)
  }
  fpc <- as.matrix(df)
  if (xor(ispopsize <- any(df > 1), all(df >= 1))) {
    big <- which(fpc >= 1, arr.ind = TRUE)
    small <- which(fpc < 1, arr.ind = TRUE)
    cat("record", big[1, 1], " stage", big[1, 2], ": fpc=", 
      fpc[big[1, , drop = FALSE]], "\n")
    cat("record", small[1, 1], " stage ", small[1, 2], ": fpc=", 
      fpc[small[1, , drop = FALSE]], "\n")
    stop("Must have all fpc>=1 or all fpc<=1")
  }
  if (ispopsize) {
    if (pps) 
      stop("fpc must be specified as sampling fraction for PPS sampling")
    popsize <- fpc
  }
  else {
    popsize <- sampsize/(fpc)
  }
  if (any(popsize < sampsize)) {
    toobig <- which(popsize < sampsize, arr.ind = TRUE)
    cat("record", toobig[1, 1], "stage", toobig[1, 2], ": popsize=", 
      popsize[toobig[1, , drop = FALSE]], " sampsize=", 
      sampsize[toobig[1, , drop = FALSE]], "\n")
    stop("FPC implies >100% sampling in some strata")
  }
  if (!ispopsize && any(is.finite(popsize) & (popsize > 1e+10))) {
    big <- which(popsize > 1e+10 & is.finite(popsize), arr.ind = TRUE)
    warning("FPC implies population larger than ten billion (record", 
      big[1, 1], " stage ", big[1, 2], ")")
  }
  if (!pps) {
    for (i in 1:ncol(popsize)) {
      diff <- by(popsize[, i], list(strata[, i]), count)
      if (any(as.vector(diff) > 1)) {
        j <- which(as.vector(diff) > 1)[1]
        warning("`fpc' varies within strata: stratum ", 
          names(diff)[j], " at stage ", i)
      }
    }
  }
  else {
    diff <- by(popsize[, i], list(ids[, i]), count)
    if (any(as.vector(diff) > 1)) {
      j <- which(as.vector(diff) > 1)[1]
      warning("`fpc' varies within cluster: cluster ", 
        names(diff)[j], " at stage ", i)
    }
  }
  rval <- list(popsize = popsize, sampsize = sampsize)
  class(rval) <- "survey_fpc"
  rval
}

[smishr]

designs updated too much