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# This R package is free software; you can redistribute it and/or
# modify it under the terms of the GNU Library General Public
# License as published by the Free Software Foundation; either
# version 2 of the License, or (at your option) any later version.
#
# This R package is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Library General Public License for more details.
#
# You should have received a copy of the GNU Library General
# Public License along with this R package; if not, write to the
# Free Foundation, Inc., 59 Temple Place, Suite 330, Boston,
# MA 02111-1307 USA
################################################################################
# FUNCTION: DESCRIPTION:
# skewness Returns a number which is the skewness of the data
# skewness.default Default method
# skewness.data.frame Method for objects of class data.frame
# skewness.POSIXct Method for objects of class POSIXct
# skewness.POSIXlt Method for objects of class POSIXlt
################################################################################
# ---------------------------------------------------------------------------- #
# Roxygen Tags
#' @export
# ---------------------------------------------------------------------------- #
skewness <-
function (x, ...)
{
# A function implemented by Diethelm Wuertz
# FUNCTION:
# Return Value:
UseMethod("skewness")
}
# ---------------------------------------------------------------------------- #
# Roxygen Tags
#' @export
# ---------------------------------------------------------------------------- #
skewness.default <-
function (x, na.rm = FALSE, method = c("moment", "fisher"), ...)
{
# A function implemented by Diethelm Wuertz
# Description:
# Returns the value of the skewness of a distribution function.
# Details:
# Missing values can be handled.
# FUNCTION:
# Method:
method = match.arg(method)
# Warnings:
if (!is.numeric(x) && !is.complex(x) && !is.logical(x)) {
warning("argument is not numeric or logical: returning NA")
return(as.numeric(NA))}
stopifnot(NCOL(x) == 1)
# Remove NAs:
if (na.rm) x = x[!is.na(x)]
# Skewness:
n = length(x)
if (is.integer(x)) x = as.numeric(x)
# Selected Method:
if (method == "moment") {
skewness = sum((x-mean(x))^3/sqrt(as.numeric(var(x)))^3)/length(x)
}
if (method == "fisher") {
if (n < 3)
skewness = NA
else
skewness = ((sqrt(n*(n-1))/(n-2))*(sum(x^3)/n))/((sum(x^2)/n)^(3/2))
}
# Add Control Attribute:
attr(skewness, "method") <- method
# Return Value:
skewness
}
# ---------------------------------------------------------------------------- #
# Roxygen Tags
#' @export
# ---------------------------------------------------------------------------- #
skewness.data.frame <-
function (x, na.rm = FALSE, method = c("moment", "fisher"), ...)
{
# A function implemented by Diethelm Wuertz
## Amended by Georgi N. Boshnakov to set attribute 'method' as documented.
## (changed the signature from (x, ...) to make this straightforward)
# FUNCTION:
method <- match.arg(method)
# Return Value:
structure(sapply(x, skewness, na.rm = na.rm, method = method, ...),
method = method)
}
# ---------------------------------------------------------------------------- #
# Roxygen Tags
#' @export
# ---------------------------------------------------------------------------- #
skewness.POSIXct <-
function (x, ...)
{
# A function implemented by Diethelm Wuertz
# FUNCTION:
# Return Value:
structure(skewness(unclass(x), ...), oldClass(x))
}
# ---------------------------------------------------------------------------- #
# Roxygen Tags
#' @export
# ---------------------------------------------------------------------------- #
skewness.POSIXlt <-
function (x, ...)
{
# A function implemented by Diethelm Wuertz
# FUNCTION:
# Return Value:
as.POSIXlt(skewness(as.POSIXct(x), ...))
}
################################################################################
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