density(x, bw, adjust = 1, kernel="gaussian", window = kernel, n = 512, width, from, to, cut = 3, na.rm = FALSE) print(dobj) plot(dobj, main = NULL, xlab = NULL, ylab = "Density", type = "l", zero.line = TRUE, ...)
x
| the data from which the estimate is to be computed. |
n
|
the number of equally spaced points at which the density
is to be estimated. When n > 512 , it is rounded up to the next
power of 2 for efficieny reasons (fft ).
|
kernel,window
|
a character string giving the smoothing kernel to be used.
This must be one of "gaussian" , "rectangular" ,
"triangular" , or "cosine" , and may be abbreviated to a
single letter.
|
bw
|
the smoothing bandwith to be used. This is the standard
deviation of the smoothing kernel. It defaults to 0.9 times the
minimum of the standard deviation and the interquartile range divided by
1.34 times the sample size to the negative one fifth power
(= Silverman's ``rule of thumb'').
The specified value of bw is multiplied by adjust .
|
adjust
|
the bandwith used is actually adjust*bw .
This makes it easy to specify values like ``half the default'' bandwidth.
|
width
| this exists for compatibility with S. |
from,to
| the left and right-most points of the grid at which the density is to be estimated. |
cut
|
by default, the values of left and right are
cut bandwidths beyond the extremes of the data. This allows the
estimated density to drop to approximately zero at the extremes.
|
na.rm
|
logical; if TRUE , missing values are eliminated from
x in advance to further computation.
|
dobj
| a ``density'' object. |
main, xlab, ylab, type
| plotting parameters with useful defaults. |
...
| further plotting parameters. |
zero.line
|
logical; if TRUE , add a base line at y = 0
|
density
computes kernel density estimates
with the given kernel and bandwidth.
The generic functions plot
and print
have
methods for density objects.
density
disperses the mass of the
empirical distribution function over a regular grid of at least 512
points and then
uses the fast Fourier transform to convolve this approximation
with a discretized version of the kernel and then uses linear
approximation to evaluate the density at the specified points."density"
.
The underlying structure is a list containing the following components.
x
|
the n coordinates of the points where the density is estimated.
|
y
| the estimated density values. |
bw
| the bandwidth used. |
N
|
the sample size length(x) .
|
call
| the call which produced the result. |
data.name
|
the deparsed name of the x argument.
|
has.na
|
logical, indicating if there were NA s in the
sample and na.rm == FALSE .
|
Venables, W. N. and B. D. Ripley (1994). Modern Applied Statistics with S-Plus. New York: Springer.
Scott, D. W. (1992). Multivariate Density Estimation. Theory, Practice and Visualization. New York: Wiley.
Sheather, S. J. and M. C. Jones (1991). ``A reliable data-based bandwidth selection method for kernel density estimation. J. Roy. Statist. Soc. B, 683-690.
convolve
, hist
.# The Old Faithful geyser data data(faithful) d <- density(faithful$eruptions, bw=0.15) d plot(d) plot(d, type="n") polygon(d, col="wheat") ## Missing values: x <- xx <- faithful$eruptions x[i.out <- sample(length(x), 10)] <- NA doR <- density(x, bw=0.15, na.rm = TRUE) doN <- density(x, bw=0.15, na.rm = FALSE) lines(doR, col="blue") lines(doN, col="red") points(xx[i.out], rep(.01,10))