generate_combinations.R

#' Create unique combinations
#' 
#' To a given vector of numeric values add or subtract a constant value,
#' and return all possible combinations of that as a matrix
#' 
#' @param values a vector with numeri values
#' @param change_value a numeric value too add or subtract
#' 
#' @details
#' There are 2^length(values) possible combinations
#' 
#' @examples
#' generate_combinations(c(1,2,3), .1)
#' 

generate_combinations <- function(values, change_value = 0.1) {
  
  if(!is.numeric(values)) stop("values must be a numeric vector")
  if(!is.numeric(change_value)) stop("change_value must be numeric")
  
  all_changes <- c(change_value, -change_value)
  combinations <- expand.grid(rep(list(all_changes), length(values)))
  vectorized <- as.numeric(t(combinations)) + values
  final <- matrix(vectorized, byrow=TRUE, ncol=length(values))
  
  return(final)
  
}