R/rmixgamma.R

In mixR: Finite Mixture Modeling for Raw and Binned Data

#' Generating Random Data From A Gamma Mixture Model
#'
#' The function \code{rmixgamma} generates random data from a Gamma mixture model.
#'
#' The number of random data from each component \eqn{n_0} (a vector) is generated from a multinomial
#' distribution Multinom\eqn{(n, pi)}. Then the random data from each component is generated with
#' the sample sized specified in \eqn{n_0} and parameters of Gamma distributions specified in
#' \code{mu} and \code{sd}.
#'
#' @param n a positive integer specifying the number of observations we want to generate from the mixture model
#' @param pi a numeric vector for the proportion of each component
#' @param mu a numeric vector for the mean of each component
#' @param sd a numeric vector for the standard deviation of each component
#'
#' @return The function \code{rmixgamma} returns a numeric vector of random data from the specified Gamma mixture model.
#'
#' @seealso \code{\link{rmixnormal}}, \code{\link{rmixweibull}}, \code{\link{rmixlnorm}}
#'
#' @examples
#' x <- rmixgamma(1000, c(0.4, 0.6), c(2, 5), c(1, 0.5))
#' hist(x, breaks = 40)
#'
#' @export
rmixgamma <- function(n, pi, mu, sd) {
  if(!(is.numeric(n) || is.numeric(pi) || is.numeric(mu) || is.numeric(sd)))
  {stop("numeric inputs are required.")}
  if(length(pi) != length(mu) || (length(pi) != length(sd)))
  {stop("'pi', 'mu' and 'sd' should have the same length.")}
  if(any(c(n < 0, pi < 0, sd < 0)))
  {stop("positive 'n', 'pi' and 'sd' are required.")}
  if(length(n) > 1) stop("'n' should be a positive integer.")

	n0 <- rmultinom(1, n, pi)[, 1]
	pars <- to_shape_rate_gamma(mu, sd)
	alpha <- pars[[1]]
	lambda <- pars[[2]]
	res <- numeric(0)
	for(i in 1:length(pi)) {
		tmp <- rgamma(n0[i], alpha[i], lambda[i])
		res <- c(res, tmp)
	}
	res
}