R/var.fdt.R

In fdth: Frequency Distribution Tables, Histograms and Polygons

var.fdt <- function(x, ...)
{
  brk <- with(x,
              seq(breaks['start'],
                  breaks['end'],
                  breaks['h']))

  mids <- 0.5 * (brk[-1] + 
                 brk[-length(brk)])

  y <- with(x,
            table[, 2])

  res <- sum((mids - mean.fdt(x))^2 * y) / (sum(y) - 1)

  return(res)
}