rPref (version 0.6)

get_btg: Better-Than-Graph

Description

Returns a Hasse-Diagramm of a preference order (also called the Better-Than-Graph) on a given data set to be plotted with the igraph package or plots the graph directly.

Usage

get_btg(df, pref, flip.edges = FALSE)
plot_btg(df, pref, labels = 1:nrow(df), flip.edges = FALSE)

Arguments

df

A data frame.

pref

A preference on the columns of df, see psel for details.

flip.edges

(optional) Flips the orientation of edges, if TRUE than arrows point from worse nodes to better nodes.

labels

(optional) Labels for the vertices when plot_btg is used.

Details

The function get_btg returns a list l with the following list entries:

[object Object],[object Object]

To plot the resulting graph returned from get_btg, use the plot function as follows:

plot(l$graph, layout = l$layout).

For more details, see igraph.plotting and the examples below. The function plot_btg directly plots the Better-Than-Graph some defaults values for e.g., vertex size.

The Hasse diagram of a preference visualizes all the better-than-relationsships on a given data set. All edges which can be retrieved by transitivity of the order are omitted.

By default, the arrows in the diagram point from better to worse nodes w.r.t. the preference. This means an arrow can be read as "is better than". If flip.edges = TRUE is set, then the arrows point from worse nodes to better nodes ("is worse than"). In any case, the better nodes are plotted at the top and the worse nodes at the bottom of the diagram.

The names of the vertices are characters ranging from "1" to as.character(nrow(df)) and they correspond to the row numbers of df. By default, these are also the labels of the vertices. Alternatively, they can be defined manually in the plot function or using the labels parameter of plot_btg.

See Also

igraph.plotting

Examples

# pick a small data set and create preference and BTG
df <- mtcars[1:10,]
pref <- high(mpg) * low(wt)

# directly plot the BTG with row numbers as labels
plot_btg(df, pref)

# create the BTG and labels for the nodes with relevant values
btg <- get_btg(df, pref)
labels <- paste0(df$mpg, "\n", df$wt)

# plot the graph using igraph
library(igraph)
plot(btg$graph, layout = btg$layout, vertex.label = labels,
     vertex.size = 25)

# add colors for the maxima nodes and plot again
colors <- rep(rgb(1, 1, 1), nrow(df))
colors[psel.indices(df, pref)] <- rgb(0,1,0)
plot(btg$graph, layout = btg$layout, vertex.label = labels,
     vertex.size = 25, vertex.color = colors)

# show lattice structure of 3-dimensional Pareto preference
df <- merge(merge(data.frame(x = 1:3), data.frame(y = 1:3)), data.frame(z = 1:2))
labels <- paste0(df$x, ",", df$y, ",", df$z)
btg <- get_btg(df, low(x) * low(y) * low(z))
plot(btg$graph, layout = btg$layout, vertex.label = labels,
     vertex.size = 20)