R/moments.R

In burrm/lolcat: Miscellaneous Useful Functions

moment.k<-function(x, 
                   k = 2, 
                   center = mean,
                   denominator = c("n", "n-1")
) {
  n  <- length(na.omit(x))
  mp <- center(x)
  sum( (x-mp)^k / (eval(parse(text = denominator[1])))   )
}

.moment.m2 <- function(x) {
  moment.k(x,2)
}

.moment.m3 <- function(x) {
  moment.k(x,3)
}

.moment.m4 <- function(x) {
  moment.k(x,4)
}




#Test case
#moment.k(c(1,2,2,3,3,3),2)
#var(c(1,2,2,3,3,3))*5/6