getBreaks: Classification

In cartography: Thematic Cartography

Classification

Description

A function to classify continuous 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 classification method; one of "fixed", "sd", "equal", "pretty", "quantile", "kmeans", "hclust", "bclust", "fisher", "jenks", "dpih", "q6", "geom", "arith", "em" 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).
...	further arguments of classIntervals.

Details

"fixed", "sd", "equal", "pretty", "quantile", "kmeans", "hclust", "bclust", "fisher", "jenks" and "dpih" are classIntervals methods. You may need to pass additional arguments for some of them.

Jenks ("jenks" method) and Fisher-Jenks ("fisher" method) 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 "arith" method is based on an arithmetic progression along the variable values.

The "em" method is based on nested averages computation.

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.

Value

A numeric vector of breaks

Note

This function is mainly a wrapper of classIntervals + "arith", "em", "q6", "geom" and "msd" methods.

See Also

classIntervals

Examples

library(sf)
mtq <- st_read(system.file("gpkg/mtq.gpkg", package="cartography"))
var <- mtq$MED
# Histogram
hist(var, probability = TRUE, breaks = 20)
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)

# Pretty breaks
breaks <- getBreaks(v = var, nclass = 4, method = "pretty")
hist(var, probability = TRUE, breaks = breaks, col = "#F0D9F9", axes = FALSE)
rug(var)
axis(1, at = breaks)
axis(2)
abline(v = med, col = "blue", lwd = 6)

# kmeans method
breaks <- getBreaks(v = var, nclass = 4, method = "kmeans")
hist(var, probability = TRUE, breaks = breaks, col = "#F0D9F9")
rug(var)
abline(v = med, col = "blue", lwd = 6)

# 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)

cartography documentation built on Sept. 14, 2023, 5:08 p.m.