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Plot a Quantile Function

Source: R/geom_qf.R
geom_qf.Rd

geom_qf() creates a ggplot2 layer that plots a quantile function (inverse CDF) as a line. It computes quantile values for a sequence of probabilities (from 0 to 1) and connects them with a line.

Usage

geom_qf(
  mapping = NULL,
  data = NULL,
  stat = StatQF,
  position = "identity",
  ...,
  na.rm = FALSE,
  show.legend = NA,
  inherit.aes = TRUE,
  fun = NULL,
  cdf_fun = NULL,
  pdf_fun = NULL,
  survival_fun = NULL,
  n = 101,
  args = list()
)

StatQF

Format

An object of class StatQF (inherits from Stat, ggproto, gg) of length 2.

Arguments

mapping

Set of aesthetic mappings created by aes(). If specified and inherit.aes = TRUE (the default), it is combined with the default mapping at the top level of the plot. You must supply mapping if there is no plot mapping.

data

Ignored by stat_function(), do not use.

stat

The statistical transformation to use on the data for this layer. When using a geom_*() function to construct a layer, the stat argument can be used to override the default coupling between geoms and stats. The stat argument accepts the following:

  • A Stat ggproto subclass, for example StatCount.

  • A string naming the stat. To give the stat as a string, strip the function name of the stat_ prefix. For example, to use stat_count(), give the stat as "count".

  • For more information and other ways to specify the stat, see the layer stat documentation.

position

A position adjustment to use on the data for this layer. This can be used in various ways, including to prevent overplotting and improving the display. The position argument accepts the following:

  • The result of calling a position function, such as position_jitter(). This method allows for passing extra arguments to the position.

  • A string naming the position adjustment. To give the position as a string, strip the function name of the position_ prefix. For example, to use position_jitter(), give the position as "jitter".

  • For more information and other ways to specify the position, see the layer position documentation.

...

Other parameters passed on to ggplot2::layer().

na.rm

If FALSE, the default, missing values are removed with a warning. If TRUE, missing values are silently removed.

show.legend

Logical. Should this layer be included in the legends? NA, the default, includes if any aesthetics are mapped. FALSE never includes, and TRUE always includes. It can also be a named logical vector to finely select the aesthetics to display. To include legend keys for all levels, even when no data exists, use TRUE. If NA, all levels are shown in legend, but unobserved levels are omitted.

inherit.aes

If FALSE, overrides the default aesthetics, rather than combining with them. This is most useful for helper functions that define both data and aesthetics and shouldn't inherit behaviour from the default plot specification, e.g. annotation_borders().

fun

A function to compute the quantile function (e.g. qnorm). The function must accept a numeric vector of probabilities (values in [0,1]) as its first argument. Exactly one of fun, cdf_fun, pdf_fun, or survival_fun must be provided.

cdf_fun

A CDF function (e.g. pnorm). The quantile function is derived numerically via root-finding. Exactly one of fun, cdf_fun, pdf_fun, or survival_fun must be provided.

pdf_fun

A PDF function (e.g. dnorm). The CDF is first derived by numerical integration, then the quantile function by root-finding. Exactly one of fun, cdf_fun, pdf_fun, or survival_fun must be provided.

survival_fun

A survival function (e.g. function(x) 1 - pnorm(x)). The CDF is computed as \(F(x) = 1 - S(x)\) and then the quantile function is derived by root-finding. Exactly one of fun, cdf_fun, pdf_fun, or survival_fun must be provided.

n

Number of probability points at which to evaluate fun. Defaults to 101. Points are placed at Chebyshev nodes of the first kind on $(0, 1)$, which cluster near 0 and 1 where quantile functions are typically most curved, and never include the exact endpoints (avoiding \(\pm\infty\) for unbounded distributions).

args

A named list of additional arguments to pass to fun, cdf_fun, or pdf_fun.

Value

A ggplot2 layer.

Details

Supply exactly one of fun (a quantile function), cdf_fun (a CDF), pdf_fun (a PDF), or survival_fun (a survival function). When cdf_fun is supplied, the quantile function is derived by numerical root-finding. When pdf_fun is supplied, the CDF is first derived by numerical integration and then inverted. When survival_fun is supplied, the CDF is computed as \(F(x) = 1 - S(x)\) and then inverted.

Examples

  ggplot() +
    geom_qf(fun = qnorm, args = list(mean = 3, sd = 2))


  ggplot() +
    geom_qf(fun = qbeta, args = list(shape1 = 3, shape2 = 4))