distribution_parts: Find a percentage of a distribution

In coursekata: Packages and Functions for 'CourseKata' Courses

Find a percentage of a distribution

Description

Given a distribution, find which values lie in the upper, lower, or middle proportion of the distribution. Useful when you want to do something like shade in the middle 95% of a plot. This is a greedy operation, meaning that if the cutoff point is between two whole numbers the specified region will suck up the extra space. For example, the requesting the upper 30% of the ⁠[1 2 3 4]⁠ will return ⁠[FALSE FALSE TRUE TRUE]⁠ because the 30% was greedy.

outer() marks values in both outer tails of a distribution. It is the complement of middle(): outer(x, prop) is equivalent to tails(x, 1 - prop).

Usage

middle(x, prop = 0.95, greedy = TRUE)

tails(x, prop = 0.95, greedy = TRUE)

outer(x, prop)

lower(x, prop = 0.025, greedy = TRUE)

upper(x, prop = 0.025, greedy = TRUE)

Arguments

x	The distribution of values to check.
prop	The total proportion in both tails combined, must be in (0, 1).
greedy	Whether the function should be greedy, as per the description above.

Details

Note that NA values are ignored, i.e. they will always return FALSE.

Value

A logical vector indicating which values are in the specified region.

Examples

upper(1:10, .1)
lower(1:10, .2)
middle(1:10, .5)
tails(1:10, .5)

sampling_distribution <- do(1000) * mean(rnorm(100, 5, 10))
sampling_distribution %>%
  gf_histogram(~mean, data = sampling_distribution, fill = ~ middle(mean, .68)) %>%
  gf_refine(scale_fill_manual(values = c("blue", "coral")))

coursekata documentation built on March 11, 2026, 1:06 a.m.