Sample using a gamma distribution

Sample from a gamma distribution using the expected value in x and the standard deviation in sd. The gamma shape and scale parameters are derived from the input mean and standard deviation.

Usage

sample_gamma(x, sd = 1)

Arguments

x

A numeric vector of observations to sample from. If a single value is provided, it will be recycled to the length of sd. Otherwise, it must be the same length as sd.

sd

A numeric vector of standard deviations to use in rgamma(). If a single value is provided, it will be recycled to the length of x. Otherwise, it must be the same length as x.

Value

A numeric vector of the same length as x is returned.

Details

The gamma distribution is parameterized by shape and scale. Given an expected value x and a standard deviation sd, the shape parameter is calculated as x^2 / sd^2 and the scale parameter as sd^2 / x.

Examples

set.seed(123)
sample_gamma(1, sd = 1)
#> [1] 0.1822171
set.seed(123)
sample_gamma(1, sd = c(0, 1))
#> [1] 1.0000000 0.1822171
sample_gamma(1:5, sd = 1)
#> [1] 1.6957511 0.5263902 2.9603714 5.7468949 5.3669060