R: A quantile-quantile plot

geom_qq_line {ggplot2}

R Documentation

A quantile-quantile plot

Description

geom_qq and stat_qq produce quantile-quantile plots. geom_qq_line and stat_qq_line compute the slope and intercept of the line connecting the points at specified quartiles of the theoretical and sample distributions.

Usage

geom_qq_line(mapping = NULL, data = NULL, geom = "path",
  position = "identity", ..., distribution = stats::qnorm,
  dparams = list(), line.p = c(0.25, 0.75), fullrange = FALSE,
  na.rm = FALSE, show.legend = NA, inherit.aes = TRUE)

stat_qq_line(mapping = NULL, data = NULL, geom = "path",
  position = "identity", ..., distribution = stats::qnorm,
  dparams = list(), line.p = c(0.25, 0.75), fullrange = FALSE,
  na.rm = FALSE, show.legend = NA, inherit.aes = TRUE)

geom_qq(mapping = NULL, data = NULL, geom = "point",
  position = "identity", ..., distribution = stats::qnorm,
  dparams = list(), na.rm = FALSE, show.legend = NA, inherit.aes = TRUE)

stat_qq(mapping = NULL, data = NULL, geom = "point",
  position = "identity", ..., distribution = stats::qnorm,
  dparams = list(), na.rm = FALSE, show.legend = NA, inherit.aes = TRUE)

Arguments

`mapping`	Set of aesthetic mappings created by `aes()` or `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`	The data to be displayed in this layer. There are three options: If `NULL`, the default, the data is inherited from the plot data as specified in the call to `ggplot()`. A `data.frame`, or other object, will override the plot data. All objects will be fortified to produce a data frame. See `fortify()` for which variables will be created. A `function` will be called with a single argument, the plot data. The return value must be a `data.frame.`, and will be used as the layer data.
`geom`	The geometric object to use display the data
`position`	Position adjustment, either as a string, or the result of a call to a position adjustment function.
`...`	Other arguments passed on to `layer()`. These are often aesthetics, used to set an aesthetic to a fixed value, like `color = "red"` or `size = 3`. They may also be parameters to the paired geom/stat.
`distribution`	Distribution function to use, if x not specified
`dparams`	Additional parameters passed on to `distribution` function.
`line.p`	Vector of quantiles to use when fitting the Q-Q line, defaults defaults to `c(.25, .75)`.
`fullrange`	Should the q-q line span the full range of the plot, or just the data
`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.
`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. `borders()`.

Aesthetics

stat_qq understands the following aesthetics (required aesthetics are in bold):

sample
group
x
y

Learn more about setting these aesthetics in vignette("ggplot2-specs")

stat_qq_line understands the following aesthetics (required aesthetics are in bold):

sample
group
x
y

Learn more about setting these aesthetics in vignette("ggplot2-specs")

Computed variables

Variables computed by stat_qq:

sample: sample quantiles
theoretical: theoretical quantiles

Variables computed by stat_qq_line:

x: x-coordinates of the endpoints of the line segment connecting the points at the chosen quantiles of the theoretical and the sample distributions
y: y-coordinates of the endpoints

Examples


df <- data.frame(y = rt(200, df = 5))
p <- ggplot(df, aes(sample = y))
p + stat_qq() + stat_qq_line()

# Use fitdistr from MASS to estimate distribution params
params <- as.list(MASS::fitdistr(df$y, "t")$estimate)
ggplot(df, aes(sample = y)) +
  stat_qq(distribution = qt, dparams = params["df"]) +
  stat_qq_line(distribution = qt, dparams = params["df"])

# Using to explore the distribution of a variable
ggplot(mtcars, aes(sample = mpg)) +
  stat_qq() +
  stat_qq_line()
ggplot(mtcars, aes(sample = mpg, colour = factor(cyl))) +
  stat_qq() +
  stat_qq_line()

[Package ggplot2 version 3.0.0 Index]