ggdist: cut_cdf_qi – R documentation

Become an expert in R — Interactive courses, Cheat Sheets, certificates and more!

cut_cdf_qi

Categorize values from a CDF into quantile intervals

Description

Given a vector of probabilities from a cumulative distribution function (CDF) and a list of desired quantile intervals, return a vector categorizing each element of the input vector according to which quantile interval it falls into. Useful for drawing slabs with intervals overlaid on the density, e.g. using stat_halfeye() or stat_dist_halfeye()

Usage

cut_cdf_qi(p, .width = c(0.66, 0.95, 1), labels = NULL)

Arguments

p

A numeric vector of values from a cumulative distribution function, such as values returned by p-prefixed distribution functions in base R (e.g. pnorm()), the cdf() function, or values of the cdf computed aesthetic from the stat_sample_slabinterval() or stat_dist_slabinterval() stats.

.width

vector of probabilities to use that determine the widths of the resulting intervals.

labels

One of:

NULL to use the default labels (.width converted to a character vector).
A character vector giving labels (must be same length as .width)
A function that takes numeric probabilities as input and returns labels as output (a good candidate might be scales::percent_format()).

Value

An ordered factor of the same length as p giving the quantile interval to which each value of p belongs.

Examples

library(ggplot2)
library(dplyr)
library(scales)
library(distributional)

theme_set(theme_ggdist())

# with a slab
tibble(x = dist_normal(0, 1)) %>%
  ggplot(aes(dist = x, y = "a")) +
  stat_dist_slab(aes(
    fill = stat(cut_cdf_qi(cdf))
  )) +
  scale_fill_brewer(direction = -1, na.value = "gray90")

# With a halfeye (or other geom with slab and interval), NA values will
# show up in the fill scale from the CDF function applied to the internal
# interval geometry data and can be ignored, hence na.translate = FALSE
tibble(x = dist_normal(0, 1)) %>%
  ggplot(aes(dist = x, y = "a")) +
  stat_dist_halfeye(aes(
    fill = stat(cut_cdf_qi(cdf, .width = c(.5, .8, .95, 1)))
  )) +
  scale_fill_brewer(direction = -1, na.translate = FALSE)

# we could also use the labels parameter to apply nicer formatting
# and provide a better name for the legend, and omit the 100% interval
# if desired
tibble(x = dist_normal(0, 1)) %>%
  ggplot(aes(dist = x, y = "a")) +
  stat_dist_halfeye(aes(
    fill = stat(cut_cdf_qi(cdf, .width = c(.5, .8, .95), labels = percent_format(accuracy = 1)))
  )) +
  labs(fill = "Interval") +
  scale_fill_brewer(direction = -1, na.translate = FALSE)

ggdist

Visualizations of Distributions and Uncertainty

v2.4.0

GPL (>= 3)

Authors

Matthew Kay [aut, cre]

Initial release

2021-01-03