pgr_topologicalSort - Experimental¶
pgr_topologicalSort
— Returns the linear ordering of the vertices(s) for weighted directed acyclic graphs(DAG).
In particular, the topological sort algorithm implemented by Boost.Graph.
Warning
Possible server crash
These functions might create a server crash
Warning
Experimental functions
They are not officially of the current release.
They likely will not be officially be part of the next release:
The functions might not make use of ANY-INTEGER and ANY-NUMERICAL
Name might change.
Signature might change.
Functionality might change.
pgTap tests might be missing.
Might need c/c++ coding.
May lack documentation.
Documentation if any might need to be rewritten.
Documentation examples might need to be automatically generated.
Might need a lot of feedback from the comunity.
Might depend on a proposed function of pgRouting
Might depend on a deprecated function of pgRouting
Availability
Version 3.0.0
New experimental function
TBD
Description¶
The topological sort algorithm creates a linear ordering of the vertices such that if edge (u,v) appears in the graph, then v comes before u in the ordering.
This implementation can only be used with a directed graph with no cycles i.e. directed acyclic graph.
- The main characteristics are:
Process is valid for directed acyclic graphs only. otherwise it will throw warnings.
For optimization purposes, if there are more than one answer, the function will return one of them.
The returned values are ordered in topological order:
Running time: \(O( (V + E))\)
Signatures¶
Summary
pgr_topologicalSort(edges_sql)
RETURNS SET OF (seq, sorted_v)
OR EMPTY SET
- Example
For a directed graph
SELECT * FROM pgr_topologicalsort(
'SELECT id,source,target,cost,reverse_cost FROM edge_table1'
);
seq | sorted_v
-----+----------
1 | 0
2 | 1
3 | 3
4 | 2
(4 rows)
Parameters¶
Parameter |
Type |
Default |
Description |
---|---|---|---|
edges_sql |
|
SQL query as described above. |
Inner query¶
- edges_sql
an SQL query, which should return a set of rows with the following columns:
Column |
Type |
Default |
Description |
---|---|---|---|
id |
|
Identifier of the edge. |
|
source |
|
Identifier of the first end point vertex of the edge. |
|
target |
|
Identifier of the second end point vertex of the edge. |
|
cost |
|
Weight of the edge (source, target)
|
|
reverse_cost |
|
-1 |
Weight of the edge (target, source),
|
Where:
- ANY-INTEGER
SMALLINT, INTEGER, BIGINT
- ANY-NUMERICAL
SMALLINT, INTEGER, BIGINT, REAL, FLOAT
Result Columns¶
Returns set of (seq, sorted_v)
Column |
Type |
Description |
---|---|---|
seq |
|
Sequential value starting from 1. |
sorted_v |
|
Linear ordering of the vertices(ordered in topological order) |
See Also¶
The queries use the Sample Data network.
Indices and tables