Extract x and y values from cdplot() - r

Question

How can I extract the exact probabilities for each factor y at any value of x with cdplot(y~x)
Thanks

Answer 1

Following the example from the help file of ?cdplot you can do...
## NASA space shuttle o-ring failures
fail <- factor(c(2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 2, 1, 2, 1, 1, 1,
1, 2, 1, 1, 1, 1, 1),
levels = 1:2, labels = c("no", "yes"))
temperature <- c(53, 57, 58, 63, 66, 67, 67, 67, 68, 69, 70, 70,
70, 70, 72, 73, 75, 75, 76, 76, 78, 79, 81)
## CD plot
result <- cdplot(fail ~ temperature)
And this is a simple way to obtain the probabilities from the cdplot output.
# Getting the probabilities for each group.
lapply(split(temperature, fail), result[[1]])
$no
[1] 0.8166854 0.8209055 0.8209055 0.8209055 0.8090438 0.7901473 0.7718317 0.7718317 0.7579343
[10] 0.7664731 0.8062898 0.8326761 0.8326761 0.8905854 0.9185472 0.9626185
$yes
[1] 3.656304e-05 6.273653e-03 1.910046e-02 6.007471e-01 7.718317e-01 7.718317e-01 8.062898e-01
Note that result is a conditional density function (cumulative over the levels of fail) returned invisibly by cdplot, therefore we can split temperature by fail and apply the returned function over those values using lapply.

Answer 2

Here a simple version of getS3method('cdplot','default') :
get.props <- function(x,y,n){
ny <- nlevels(y)
yprop <- cumsum(prop.table(table(y)))
dx <- density(x, n )
y1 <- matrix(rep(0, n * (ny - 1L)), nrow = (ny - 1L))
rval <- list()
for (i in seq_len(ny - 1L)) {
dxi <- density(x[y %in% levels(y)[seq_len(i)]],
bw = dx$bw, n = n, from = min(dx$x), to = max(dx$x))
y1[i, ] <- dxi$y/dx$y * yprop[i]
}
}