Categorize values from a CDF into quantile intervals

Source: R/cut_cdf_qi.R

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().

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_slabinterval() family of 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.

See also

See stat_slabinterval() and its shortcut stats, which generate cdf aesthetics that can be used with cut_cdf_qi() to draw slabs colored by their intervals.

Examples


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

theme_set(theme_ggdist())

# with a slab
tibble(x = dist_normal(0, 1)) %>%
  ggplot(aes(xdist = x)) +
  stat_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(xdist = x)) +
  stat_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(xdist = x)) +
  stat_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)