topological_sort(G)
A topological sort is a nonunique permutation of the nodes of a directed graph such that an edge from u to v implies that u appears before v in the topological sort order. This ordering is valid only if the graph has no directed cycles.
This algorithm is based on a description and proof in "Introduction to Algorithms: A Creative Approach" .
A directed acyclic graph (DAG)
Topological sort is defined for directed graphs only. If the graph G is undirected, a NetworkXError
is raised.
If G is not a directed acyclic graph (DAG) no topological sort exists and a NetworkXUnfeasible
exception is raised. This can also be raised if G is changed while the returned iterator is being processed
If G is changed while the returned iterator is being processed.
Returns a generator of nodes in topologically sorted order.
Yields the nodes in topological sorted order.
To get the reverse order of the topological sort:
>>> DG = nx.DiGraph([(1, 2), (2, 3)])
... list(reversed(list(nx.topological_sort(DG)))) [3, 2, 1]
If your DiGraph naturally has the edges representing tasks/inputs and nodes representing people/processes that initiate tasks, then topological_sort is not quite what you need. You will have to change the tasks to nodes with dependence reflected by edges. The result is a kind of topological sort of the edges. This can be done with networkx.line_graph
as follows:
>>> list(nx.topological_sort(nx.line_graph(DG))) [(1, 2), (2, 3)]See :
The following pages refer to to this document either explicitly or contain code examples using this.
networkx.algorithms.dag.topological_sort
networkx.algorithms.dag.lexicographical_topological_sort
networkx.algorithms.dag.is_directed_acyclic_graph
networkx.algorithms.dag.topological_generations
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