cdplot
Conditional Density Plots
Computes and plots conditional densities describing how the
conditional distribution of a categorical variable y
changes over a
numerical variable x
.
 Keywords
 hplot
Usage
cdplot(x, ...)
"cdplot"(x, y, plot = TRUE, tol.ylab = 0.05, ylevels = NULL, bw = "nrd0", n = 512, from = NULL, to = NULL, col = NULL, border = 1, main = "", xlab = NULL, ylab = NULL, yaxlabels = NULL, xlim = NULL, ylim = c(0, 1), ...)
"cdplot"(formula, data = list(), plot = TRUE, tol.ylab = 0.05, ylevels = NULL, bw = "nrd0", n = 512, from = NULL, to = NULL, col = NULL, border = 1, main = "", xlab = NULL, ylab = NULL, yaxlabels = NULL, xlim = NULL, ylim = c(0, 1), ..., subset = NULL)
Arguments
 x
 an object, the default method expects a single numerical variable (or an object coercible to this).
 y
 a
"factor"
interpreted to be the dependent variable  formula
 a
"formula"
of typey ~ x
with a single dependent"factor"
and a single numerical explanatory variable.  data
 an optional data frame.
 plot
 logical. Should the computed conditional densities be plotted?
 tol.ylab
 convenience tolerance parameter for yaxis annotation. If the distance between two labels drops under this threshold, they are plotted equidistantly.
 ylevels
 a character or numeric vector specifying in which order the levels of the dependent variable should be plotted.
 bw, n, from, to, ...
 arguments passed to
density
 col
 a vector of fill colors of the same length as
levels(y)
. The default is to callgray.colors
.  border
 border color of shaded polygons.
 main, xlab, ylab
 character strings for annotation
 yaxlabels
 character vector for annotation of y axis, defaults to
levels(y)
.  xlim, ylim
 the range of x and y values with sensible defaults.
 subset
 an optional vector specifying a subset of observations to be used for plotting.
Details
cdplot
computes the conditional densities of x
given
the levels of y
weighted by the marginal distribution of y
.
The densities are derived cumulatively over the levels of y
.
This visualization technique is similar to spinograms (see spineplot
)
and plots $P(y  x)$ against $x$. The conditional probabilities
are not derived by discretization (as in the spinogram), but using a smoothing
approach via density
.
Note, that the estimates of the conditional densities are more reliable for highdensity regions of $x$. Conversely, the are less reliable in regions with only few $x$ observations.
Value

The conditional density functions (cumulative over the levels of
y
)
are returned invisibly.
References
Hofmann, H., Theus, M. (2005), Interactive graphics for visualizing conditional distributions, Unpublished Manuscript.
See Also
Examples
library(graphics)
## NASA space shuttle oring 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
cdplot(fail ~ temperature)
cdplot(fail ~ temperature, bw = 2)
cdplot(fail ~ temperature, bw = "SJ")
## compare with spinogram
(spineplot(fail ~ temperature, breaks = 3))
## highlighting for failures
cdplot(fail ~ temperature, ylevels = 2:1)
## scatter plot with conditional density
cdens < cdplot(fail ~ temperature, plot = FALSE)
plot(I(as.numeric(fail)  1) ~ jitter(temperature, factor = 2),
xlab = "Temperature", ylab = "Conditional failure probability")
lines(53:81, 1  cdens[[1]](53:81), col = 2)