R/combineStrata.R

In omopgenerics: Methods and Classes for the OMOP Common Data Model

# Copyright 2024 DARWIN EU (C)
#
# This file is part of omopgenerics
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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#' Provide all combinations of strata levels.
#'
#' @param levels Vector of all strata levels to combine.
#' @param overall Whether to provide an empty element `character()`.
#'
#' @return A vector of all combinations of strata.
#' @export
#' @examples
#'
#' combineStrata(character())
#' combineStrata(character(), overall = TRUE)
#' combineStrata(c("age", "sex"), overall = TRUE)
#' combineStrata(c("age", "sex", "year"))
#'
combineStrata <- function(levels,
                          overall = FALSE) {
  # Checks
  assertCharacter(levels, null = TRUE, na = TRUE)

  # Apply combn function to all lengths of combinations
  result <- seq_along(levels) |>
    purrr::map(\(x) utils::combn(x = levels, m = x, simplify = FALSE)) |>
    purrr::list_flatten()

  if (overall) {
    result <- c(list(character()), result)
  }

  return(result)
}