quantilefun | R Documentation |
Return the inverse function of a cumulative distribution function.
quantilefun(x, ...)
## S3 method for class 'im'
quantilefun(x, ..., type=1)
## S3 method for class 'ecdf'
quantilefun(x, ..., type=1)
## S3 method for class 'ewcdf'
quantilefun(x, ..., type=1)
x |
Data for which the quantile function should be calculated.
Either an object containing data (of class |
... |
Other arguments passed to methods. |
type |
Integer specifying the type of quantiles,
as explained in |
Whereas the command quantile
calculates
the quantiles of a dataset corresponding to desired probabilities
p
, the command quantilefun
returns a function which can be used to compute any quantiles of the
dataset.
If f <- quantilefun(x)
then f
is a function such that
f(p)
is the quantile associated with any given probability p
.
For example f(0.5)
is the median of the original data, and
f(0.99)
is the 99th percentile of the original data.
If x
is a pixel image (object of class "im"
)
then the pixel values of x
will be extracted
and the quantile function of the pixel values is constructed.
If x
is an object representing a cumulative distribution
function (object of class "ecdf"
or "ewcdf"
) then the
quantile function of the original data is constructed.
A function in the R language.
.
ewcdf
,
quantile.ewcdf
,
ecdf
,
quantile
## numeric data
z <- rnorm(50)
FZ <- ecdf(z)
QZ <- quantilefun(FZ)
QZ(0.5) # median value of z
if(interactive()) plot(QZ, xlim=c(0,1), xlab="probability",
ylab="quantile of z")
## image data
Z <- bei.extra$elev
if(require(spatstat.explore)) {
FE <- spatialcdf(Z, normalise=TRUE)
} else {
FE <- ecdf(Z[])
}
QE <- quantilefun(FE)
QE(0.5) # median elevation
if(interactive()) plot(QE, xlim=c(0,1),
xlab="probability", ylab="quantile of elevation")
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