venn (version 1.12)

getZones: Calculate the union(s) of set intersections.

Description

This function uses a metacommand to calculate the shape of a specific zone or a list of zones.

Usage

getZones(area, snames, ellipse = FALSE)

Value

A list of self-enclosed polygons, for each independent zone.

Arguments

area

A character expression written in sum of products form.

snames

A string containing the sets' names, separated by commas.

ellipse

Logical, get the zones from the shape of an ellipse, where possible

Details

A SOP ("sum of products") is also known as a DNF ("disjunctive normal form"), or in other words a "union of intersections", for example A*D + B*c.

The same expression can be written in curly brackets notation: A{1}*D{1} + B{1}*C{0}.

The expression B{1}*C{0} can also be written in a pseudo-language, as "-10-" (assuming there are only four sets).

A "zone" is a union of set intersections. There are exactly 2^k intersections in a Venn diagram, where k is the number of sets. To highlight an entire set, we need a union of all possible intersections which form that set.

The argument ellipse retrieves the data from the shape of an ellipse, and it only works with 4 and 5 sets.

Examples

venn(3)

area <- getZones("A", snames = "A, B, C")
# a list of length 1

polygon(area[[1]], col="lightblue")


# The very same result is obtained with:
zone <- getZones("1--")



# for 5 sets, the content of the 5th set but not in the first set is a
# list of two zones

venn(5)

zones <- getZones("0---1")
# this time a list of length 2

# (re)coloring the first zone (union)
polygon(zones[[1]], col="lightblue")

# and the second zone (union)
polygon(zones[[2]], col="lightblue")