bssBYcut function

Between group SS for y, for all possible splits on values of x

Each point of separation between successve values of x is used in turn to create two groups of observations. The between group sum of squares for y is calculated for each such split.

bssBYcut(x, y, data)

Arguments

• x: Variable (numeric) used to define splits. Observations with x

  values less than the cut point go into the first group, while those with values >= the cut point go into the second group.

• y: Variable for which BSS values are to be calculated.

• data: Data frame with columns x and y.

Returns

Data frame with columns: - xOrd: Cut points for splits.

• comp2: Between groups sum of squares

Author(s)

J H Maindonald

Examples

xy <- bssBYcut(weight, height, women)
with(xy, xy[which.max(bss), ])

## The function is currently defined as
function (x, y, data)
{
    xnam <- deparse(substitute(x))
    ynam <- deparse(substitute(y))
    xv <- data[, xnam]
    yv <- data[, ynam]
    sumss <- function(x, y, cut) {
        av <- mean(y)
        left <- x < cut
        sum(left) * (mean(y[left]) - av)^2 + sum(!left) * (mean(y[!left]) -
            av)^2
    }
    xOrd <- unique(sort(xv))[-1]
    bss <- numeric(length(xOrd))
    for (i in 1:length(xOrd)) {
        bss[i] <- sumss(xv, yv, xOrd[i])
    }
    list(xOrd = xOrd, bss = bss)
  }