R/ind_draw.R

In diazrenata/birdsize: Estimate Avian Body Size Distributions

#' Draw individuals to make a population.
#'
#' This is not a user-facing function; it is the random number generator
#' under-the-hood for [pop_generate].
#'
#' @param species_mean mean body size
#' @param species_sd standard deviation of body size
#' @param species_abundance number of individuals to draw
#'
#' @return vector of individuals' simulated body masses
#'
#' @importFrom truncnorm rtruncnorm
#' @importFrom stats pnorm
#' @keywords internal
ind_draw <-
  function(species_mean = NA_real_,
           species_sd = NA_real_,
           species_abundance = NA_integer_) {
    if (is.na(species_mean)) {
      stop("`species_mean` must be provided")
    }

    if (is.na(species_sd)) {
      stop("`species_sd` must be provided")
    }

    if (is.na(species_abundance)) {
      stop("`species_abundance` must be provided")
    }

    if (!is.numeric(species_abundance)) {
      stop("`species_abundance` must be numeric")
    }

    if (!(round(species_abundance) == species_abundance)) {
      stop("`species_abundance` must be a whole number")
    }

    population <-
      truncnorm::rtruncnorm(
        n = species_abundance,
        a = 1,
        b = Inf,
        mean = species_mean,
        sd = species_sd
      )


    population
  }