R/wilcox_test.R

In kassambara/rstatix: Pipe-Friendly Framework for Basic Statistical Tests

#' @include utilities.R utilities_two_sample_test.R
#' @importFrom stats wilcox.test
NULL
#'Wilcoxon Tests
#'
#'
#'@description Provides a pipe-friendly framework to performs one and two sample
#'  Wilcoxon tests. Read more:
#'  \href{https://www.datanovia.com/en/lessons/wilcoxon-test-in-r/}{Wilcoxon in
#'  R}.
#'@inheritParams stats::wilcox.test
#'@param data a data.frame containing the variables in the formula.
#'@param formula a formula of the form \code{x ~ group} where \code{x} is a
#'  numeric variable giving the data values and \code{group} is a factor with
#'  one or multiple levels giving the corresponding groups. For example,
#'  \code{formula = TP53 ~ cancer_group}.
#'@param paired a logical indicating whether you want a paired test.
#'@param ref.group a character string specifying the reference group. If
#'  specified, for a given grouping variable, each of the group levels will be
#'  compared to the reference group (i.e. control group).
#'
#'  If \code{ref.group = "all"}, pairwise two sample tests are performed for
#'  comparing each grouping variable levels against all (i.e. basemean).
#'@param mu a number specifying an optional parameter used to form the null
#'  hypothesis.
#'@param comparisons A list of length-2 vectors specifying the groups of
#'  interest to be compared. For example to compare groups "A" vs "B" and "B" vs
#'  "C", the argument is as follow: \code{comparisons = list(c("A", "B"), c("B",
#'  "C"))}
#'@param p.adjust.method method to adjust p values for multiple comparisons.
#'  Used when pairwise comparisons are performed. Allowed values include "holm",
#'  "hochberg", "hommel", "bonferroni", "BH", "BY", "fdr", "none". If you don't
#'  want to adjust the p value (not recommended), use p.adjust.method = "none".
#'
#'@param detailed logical value. Default is FALSE. If TRUE, a detailed result is
#'  shown.
#'@param ... other arguments to be passed to the function
#'  \code{\link[stats]{wilcox.test}}.
#'
#'@details - \code{pairwise_wilcox_test()} applies the standard two sample
#'  Wilcoxon test to all possible pairs of groups. This method calls the
#'  \code{\link[stats]{wilcox.test}()}, so extra arguments are accepted.
#'
#'
#'  - If a list of comparisons is specified, the result of the pairwise tests is
#'  filtered to keep only the comparisons of interest.The p-value is adjusted
#'  after filtering.
#'
#'  - For a grouped data, if pairwise test is performed, then the p-values are
#'  adjusted for each group level independently.
#'
#'
#'  - a nonparametric confidence interval and an estimator for the pseudomedian
#'  (one-sample case) or for the difference of the location parameters
#'  \code{x-y} is computed, where x and y are the compared samples or groups.
#'  The column \code{estimate} and the confidence intervals are displayed in the
#'  test result when the option \code{detailed = TRUE} is specified in the
#'  \code{wilcox_test()} and \code{pairwise_wilcox_test()} functions. Read more
#'  about the calculation of the estimate in the details section of the R base
#'  function \code{wilcox.test()} documentation by typing \code{?wilcox.test} in
#'  the R console.
#'
#'@return return a data frame with some of the following columns: \itemize{
#'  \item \code{.y.}: the y variable used in the test. \item
#'  \code{group1,group2}: the compared groups in the pairwise tests. \item
#'  \code{n,n1,n2}: Sample counts. \item \code{statistic}: Test statistic used
#'  to compute the p-value. \item \code{p}: p-value. \item \code{p.adj}: the
#'  adjusted p-value. \item \code{method}: the statistical test used to compare
#'  groups. \item \code{p.signif, p.adj.signif}: the significance level of
#'  p-values and adjusted p-values, respectively. \item \code{estimate}: an
#'  estimate of the location parameter (Only present if argument \code{detailed
#'  = TRUE}). This corresponds to the pseudomedian (for one-sample case) or to
#'  the difference of the location parameter (for two-samples case). \itemize{
#'  \item The pseudomedian of a distribution \code{F} is the median of the
#'  distribution of \code{(u+v)/2}, where \code{u} and {v} are independent, each
#'  with distribution \code{F}. If \code{F} is symmetric, then the pseudomedian
#'  and median coincide. \item Note that in the two-sample case the estimator
#'  for the difference in location parameters does not estimate the difference
#'  in medians (a common misconception) but rather the median of the difference
#'  between a sample from x and a sample from y. } \item \code{conf.low,
#'  conf.high}: a confidence interval for the location parameter. (Only present
#'  if argument conf.int = TRUE.) }
#'
#'  The \strong{returned object has an attribute called args}, which is a list
#'  holding the test arguments.
#' @examples
#' # Load data
#' #:::::::::::::::::::::::::::::::::::::::
#' data("ToothGrowth")
#' df <- ToothGrowth
#'
#' # One-sample test
#' #:::::::::::::::::::::::::::::::::::::::::
#' df %>% wilcox_test(len ~ 1, mu = 0)
#'
#'
#' # Two-samples unpaired test
#' #:::::::::::::::::::::::::::::::::::::::::
#' df %>% wilcox_test(len ~ supp)
#'
#' # Two-samples paired test
#' #:::::::::::::::::::::::::::::::::::::::::
#' df %>% wilcox_test (len ~ supp, paired = TRUE)
#'
#' # Compare supp levels after grouping the data by "dose"
#' #::::::::::::::::::::::::::::::::::::::::
#' df %>%
#'   group_by(dose) %>%
#'   wilcox_test(data =., len ~ supp) %>%
#'   adjust_pvalue(method = "bonferroni") %>%
#'   add_significance("p.adj")
#'
#' # pairwise comparisons
#' #::::::::::::::::::::::::::::::::::::::::
#' # As dose contains more than two levels ==>
#' # pairwise test is automatically performed.
#' df %>% wilcox_test(len ~ dose)
#'
#' # Comparison against reference group
#' #::::::::::::::::::::::::::::::::::::::::
#' # each level is compared to the ref group
#' df %>% wilcox_test(len ~ dose, ref.group = "0.5")
#'
#' # Comparison against all
#' #::::::::::::::::::::::::::::::::::::::::
#' df %>% wilcox_test(len ~ dose, ref.group = "all")
#'
#'@describeIn wilcox_test Wilcoxon test
#'@export
wilcox_test <- function(
  data, formula, comparisons = NULL, ref.group = NULL,
  p.adjust.method = "holm",
  paired = FALSE, exact = NULL, alternative = "two.sided",
  mu = 0, conf.level = 0.95, detailed = FALSE
)
{
  env <- as.list(environment())
  args <- env %>%
    add_item(method = "wilcox_test")
  params <- env %>%
    remove_null_items() %>%
    add_item(conf.int = TRUE, method = "wilcox.test")

  outcome <- get_formula_left_hand_side(formula)
  group <- get_formula_right_hand_side(formula)
  number.of.groups <- guess_number_of_groups(data, group)
  if(number.of.groups > 2 & !is.null(ref.group)){
    if(ref.group %in% c("all", ".all.")){
      params$data <- create_data_with_all_ref_group(data, outcome, group)
      params$ref.group <- "all"
    }
  }
  test.func <- two_sample_test
  if(number.of.groups > 2) test.func <- pairwise_two_sample_test
  do.call(test.func, params) %>%
    set_attrs(args = args) %>%
    add_class(c("rstatix_test", "wilcox_test"))
}



#'@describeIn wilcox_test performs pairwise two sample Wilcoxon test.
#'@export
pairwise_wilcox_test <- function(
  data, formula, comparisons = NULL, ref.group = NULL,
  p.adjust.method = "holm", detailed = FALSE, ...)
  {
  args <- as.list(environment()) %>%
    .add_item(method = "wilcox_test")

  res <- pairwise_two_sample_test(
    data, formula, method = "wilcox.test",
    comparisons = comparisons, ref.group = ref.group,
    p.adjust.method = p.adjust.method, detailed = detailed,
    conf.int = TRUE, ...
  )
  res %>%
    set_attrs(args = args) %>%
    add_class(c("rstatix_test", "wilcox_test"))
}