Package 'pooh'

Topological Sort

Description

Find One Total Order Consistent with Partial Order or With Directed Acyclic Graph

Usage

tsort(from, to, domain, strict = TRUE)

Arguments

from	an atomic vector
to	an atomic vector of the same mode and length as from
domain	an atomic vector of the same mode as from containing all the elements of from and to. If missing, union(from, to) is used. The domain of the relation or the nodes of the graph.
strict	logical. If TRUE then from[i] == to[i] is an error. Otherwise, such edges of the graph are ignored.

Details

Pairs (from[i], to[i]) can be though of either as elements of a relation on a set or as edges in a directed graph. This function finds one total order on the domain (nodes of the graph) that is consistent with the relation (graph) if one exists (that is if the graph is directed).

Value

A vector that is a reordering of domain so that every element of from appears in the value before the corresponding element of to.

Throws an error if there is no consistent total order (the graph has a cycle).

Examples

from <-   LETTERS[c(1, 1, 1, 1, 2, 2, 6)]
to <- LETTERS[c(2, 3, 4, 5, 3, 5, 7)]
from
to
tsort(from, to)

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Equivalence Classes

Description

Calculates Equivalence Classes

Usage

weak(from, to, domain, markers = FALSE)

Arguments

from	an atomic vector
to	an atomic vector of the same mode and length as from
domain	an atomic vector of the same mode as from containing all the elements of from and to. If missing, union(from, to) is used. The domain of the relation or the nodes of the graph.
markers	controls the type of result; see Values below.

Details

Pairs (from[i], to[i]) can be though of either as elements of a symmetric relation on a set or as edges in an undirected graph. This function calculates the equivalence classes of the transitive closure of the relation or the components of the graph. If the edges are thought of as directed, then we calculate the weak components, meaning the components of the associated undirected graph, rather than the so-called strong components of the directed graph.

Value

If markers = FALSE, a list, elements of which are the components (equivalence classes). If markers = TRUE, an integer vector of the same length as domain or as union(from, to) if domain is missing, elements of which are the same if and only if the corresponding elements of the domain (nodes of the graph) are in the same connected component (equivalence class).

Examples

to <- sample(1:100, 75, replace = TRUE)
from <- sample(1:100, 75, replace = TRUE)
out <- weak(from, to)
sapply(out, length)

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