rPref (version 0.3)

base_pref: Base preferences

Description

Base preferences are used to describe the different goals of a preference query.

Usage

low(expr)

high(expr)

true(expr)

Arguments

expr

A numerical/logical expression which is the term for the current preference. The objective is to search for minimal/maximal values of this expression (for low/high) or for logical true values (for true)

Details

Mathematically, all base preferences are strict weak orders (irreflexive, transitive and negative transitive). The three fundamental base preferences are: [object Object],[object Object] The term expr can be just a single attribute or an arbitrary expression, e.g., low(a+2*b+f(c)). There a, b and c are columns of the addressed dataset and f is a previously defined function. Functions contained in expr are evaluated over the entire dataset, i.e., it is possible to use aggregate functions (min, mean, etc.). Note that all functions (and also variables which are not columns of the dataset, where expr will be evaluated on) must be defined in the same environment (e.g. environment of a function) as the base preference.

See Also

See complex_pref how to compose complex preferences to retrieve e.g. the Skyline. See base_pref_macros for more base preferences.

Examples

# Define a preference with a score value combining mpg and hp
p1 <- high(4*mpg + hp)
# Perform the preference selection
psel(mtcars, p1)

# Define a preference with a given function
f <- function(x, y) (abs(x-mean(x))/max(x) + abs(y-mean(y))/max(y))
p2 <- low(f(mpg, hp))
psel(mtcars, p2)