entropy {segregation}

Calculates the entropy of a distribution

Description

Returns the entropy of the distribution defined by group.

Usage

entropy(data, group, weight = NULL, base = exp(1))

Arguments

data

A data frame.

group

A categorical variable or a vector of variables contained in data.

weight

Numeric. (Default NULL)

base

Base of the logarithm that is used in the entropy calculation. Defaults to the natural logarithm.

Value

A single number, the entropy.

Examples

d <- data.frame(cat = c("A", "B"), n = c(25, 75))
entropy(d, "cat", weight = "n") # => .56
# this is equivalent to -.25*log(.25)-.75*log(.75)

d <- data.frame(cat = c("A", "B"), n = c(50, 50))
# use base 2 for the logarithm, then entropy is maximized at 1
entropy(d, "cat", weight = "n", base = 2) # => 1