cartography (version 1.4.1)

getBreaks: Discretization

Description

A function to discretize continious variables.

Usage

getBreaks(v, nclass = NULL, method = "quantile", k = 1, middle = FALSE)

Arguments

v

a vector of numeric values.

nclass

a number of classes

method

a discretization method; one of "sd", "equal", "quantile", "fisher-jenks","q6", "geom" or "msd" (see Details).

k

number of standard deviation for "msd" method (see Details)..

middle

creation of a central class for "msd" method (see Details).

Value

A numeric vector of breaks

Details

"sd", "equal", "quantile" and "fisher-jenks" are classIntervals methods. Jenks and Fisher-Jenks algorithms are based on the same principle and give quite similar results but Fisher-Jenks is much faster. The "q6" method uses the following quantile probabilities: 0, 0.05, 0.275, 0.5, 0.725, 0.95, 1. The "geom" method is based on a geometric progression along the variable values. The "msd" method is based on the mean and the standard deviation of a numeric vector. The nclass parameter is not relevant, use k and middle instead. k indicates the extent of each class in share of standard deviation. If middle=TRUE then the mean value is the center of a class else the mean is a break value.

Examples

data("nuts2006")
# Create the natality rate
var <- nuts2.df$birth_2008/nuts2.df$pop2008 * 1000

# Histogram
hist(var, probability = TRUE, nclass = 30)
rug(var)
moy <- mean(var)
med <- median(var)
abline(v = moy, col = "red", lwd = 3)
abline(v = med, col = "blue", lwd = 3)

# Quantile intervals
breaks <- getBreaks(v = var, nclass = 6, method = "quantile")
hist(var, probability = TRUE, breaks = breaks, col = "#F0D9F9")
rug(var)
med <- median(var)
abline(v = med, col = "blue", lwd = 3)

# Geometric intervals
breaks <- getBreaks(v = var, nclass = 8, method = "geom")
hist(var, probability = TRUE, breaks = breaks, col = "#F0D9F9")
rug(var)

# Mean and standard deviation (msd)
breaks <- getBreaks(v = var, method = "msd", k = 1, middle = TRUE)
hist(var, probability = TRUE, breaks = breaks, col = "#F0D9F9")
rug(var)
moy <- mean(var)
sd <- sd(var)
abline(v = moy, col = "red", lwd = 3)
abline(v = moy + 0.5 * sd, col = "blue", lwd = 3)
abline(v = moy - 0.5 * sd, col = "blue", lwd = 3)