kurtosis, skewness, start with ML

R/skewness.R

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+#' Skewness of the sample
+#'
+#' @description Skewness is a measure of the asymmetry of the probability distribution of a real-valued random variable about its mean.
+#'
+#' When negative: the left tail is longer; the mass of the distribution is concentrated on the right of the figure. When positive: the right tail is longer; the mass of the distribution is concentrated on the left of the figure.
+#' @param x a vector of values, a \code{matrix} or a \code{data frame}
+#' @param na.rm a logical value indicating whether \code{NA} values should be stripped before the computation proceeds.
+#' @exportMethod skewness
+#' @seealso \code{\link{kurtosis}}
+#' @rdname skewness
+#' @export
+skewness <- function(x, na.rm = FALSE) {
+  UseMethod("skewness")
+}
+
+#' @exportMethod skewness.default
+#' @rdname skewness
+#' @export
+skewness.default <- function (x, na.rm = FALSE) {
+  x <- as.vector(x)
+  if (na.rm == TRUE) {
+    x <- x[!is.na(x)]
+  }
+  n <- length(x)
+  (base::sum((x - base::mean(x))^3) / n) / (base::sum((x - base::mean(x))^2) / n)^(3/2)
+}
+
+#' @exportMethod skewness.matrix
+#' @rdname skewness
+#' @export
+skewness.matrix <- function (x, na.rm = FALSE) {
+  base::apply(x, 2, skewness.default, na.rm = na.rm)
+}
+
+#' @exportMethod skewness.data.frame
+#' @rdname skewness
+#' @export
+skewness.data.frame <- function (x, na.rm = FALSE) {
+  base::sapply(x, skewness.default, na.rm = na.rm)
+}