pgr_topologicalSort
- Experimental¶
pgr_topologicalSort
— Linear ordering of the vertices for directed acyclic
graphs (DAG).
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
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.
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
(seq, sorted_v)
- Example:
Topologically sorting the graph
SELECT * FROM pgr_topologicalsort(
$$SELECT id, source, target, cost
FROM edges WHERE cost >= 0
UNION
SELECT id, target, source, reverse_cost
FROM edges WHERE cost < 0$$);
seq | sorted_v
-----+----------
1 | 1
2 | 5
3 | 2
4 | 4
5 | 3
6 | 13
7 | 14
8 | 15
9 | 10
10 | 6
11 | 7
12 | 8
13 | 9
14 | 11
15 | 16
16 | 12
17 | 17
(17 rows)
Parameters¶
Parameter |
Type |
Description |
---|---|---|
|
Edges SQL as described below. |
Inner Queries¶
Edges SQL¶
Column |
Type |
Default |
Description |
---|---|---|---|
|
ANY-INTEGER |
Identifier of the edge. |
|
|
ANY-INTEGER |
Identifier of the first end point vertex of the edge. |
|
|
ANY-INTEGER |
Identifier of the second end point vertex of the edge. |
|
|
ANY-NUMERICAL |
Weight of the edge ( |
|
|
ANY-NUMERICAL |
-1 |
Weight of the edge (
|
Where:
- ANY-INTEGER:
SMALLINT
,INTEGER
,BIGINT
- ANY-NUMERICAL:
SMALLINT
,INTEGER
,BIGINT
,REAL
,FLOAT
Result Columns¶
Returns set of (seq, sorted_v)
Column |
Type |
Description |
---|---|---|
|
|
Sequential value starting from \(1\) |
|
|
Linear topological ordering of the vertices |
Additional examples¶
- Example:
Topologically sorting the one way segments
SELECT * FROM pgr_topologicalsort(
$$SELECT id, source, target, cost, -1 AS reverse_cost
FROM edges WHERE cost >= 0
UNION
SELECT id, source, target, -1, reverse_cost
FROM edges WHERE cost < 0$$);
seq | sorted_v
-----+----------
1 | 5
2 | 2
3 | 4
4 | 13
5 | 14
6 | 1
7 | 3
8 | 15
9 | 10
10 | 6
11 | 7
12 | 8
13 | 9
14 | 11
15 | 12
16 | 16
17 | 17
(17 rows)
- Example:
Graph is not a DAG
SELECT * FROM pgr_topologicalsort(
$$SELECT id, source, target, cost, reverse_cost FROM edges$$);
ERROR: The graph must be a DAG.
HINT: Working with Directed Graph
CONTEXT: SQL function "pgr_topologicalsort" statement 1
See Also¶
Indices and tables