pgr_lineGraph - Experimental

pgr_lineGraph — Transforms a given graph into its corresponding edge-based graph.

Boost Graph Inside

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 2.5.0

  • New Experimental function

Description

Given a graph G, its line graph L(G) is a graph such that:

• Each vertex of L(G) represents an edge of G

• Two vertices of L(G) are adjacent if and only if their corresponding edges share a common endpoint in G.

Signatures

Summary

pgr_lineGraph(edges_sql, directed)
RETURNS SET OF (seq, source, target, cost, reverse_cost)
OR EMPTY SET

Using defaults

pgr_lineGraph(edges_sql)
RETURNS SET OF (seq, source, target, cost, reverse_cost) OR EMPTY SET

Example

For a directed graph

SELECT * FROM pgr_lineGraph(
    'SELECT id, source, target, cost, reverse_cost FROM edge_table'
);
 seq | source | target | cost | reverse_cost
-----+--------+--------+------+--------------
   1 |    -18 |     18 |    1 |            1
   2 |    -17 |     17 |    1 |            1
   3 |    -16 |     -3 |    1 |           -1
   4 |    -16 |     16 |    1 |            1
   5 |    -15 |     -9 |    1 |            1
   6 |    -15 |     15 |    1 |            1
   7 |    -14 |    -10 |    1 |            1
   8 |    -14 |     12 |    1 |           -1
   9 |    -14 |     14 |    1 |            1
  10 |    -10 |     -7 |    1 |            1
  11 |    -10 |     -4 |    1 |            1
  12 |    -10 |      8 |    1 |            1
  13 |    -10 |     10 |    1 |            1
  14 |     -9 |     -8 |    1 |            1
  15 |     -9 |      9 |    1 |            1
  16 |     -9 |     11 |    1 |           -1
  17 |     -8 |     -7 |    1 |            1
  18 |     -8 |     -4 |    1 |            1
  19 |     -8 |      8 |    1 |            1
  20 |     -7 |     -6 |    1 |            1
  21 |     -6 |      6 |    1 |            1
  22 |     -4 |     -1 |    1 |            1
  23 |     -4 |      4 |    1 |            1
  24 |     -3 |     -2 |    1 |           -1
  25 |     -3 |      5 |    1 |           -1
  26 |     -2 |     -1 |    1 |           -1
  27 |     -2 |      4 |    1 |           -1
  28 |     -1 |      1 |    1 |            1
  29 |      5 |     -8 |    1 |           -1
  30 |      5 |      9 |    1 |           -1
  31 |      5 |     11 |    1 |           -1
  32 |      7 |     -7 |    1 |            1
  33 |      7 |     -4 |    1 |            1
  34 |      8 |     11 |    1 |           -1
  35 |     10 |     12 |    1 |           -1
  36 |     11 |     13 |    1 |           -1
  37 |     12 |     13 |    1 |           -1
  38 |     13 |    -15 |    1 |           -1
  39 |     16 |     -9 |    1 |            1
  40 |     16 |     15 |    1 |            1
(40 rows)

Complete Signature

pgr_lineGraph(edges_sql, directed);
RETURNS SET OF (seq, source, target, cost, reverse_cost) OR EMPTY SET

Example

For an undirected graph

SELECT * FROM pgr_lineGraph(
    'SELECT id, source, target, cost, reverse_cost FROM edge_table',
    FALSE
);
 seq | source | target | cost | reverse_cost
-----+--------+--------+------+--------------
   1 |     -3 |     -2 |    1 |           -1
   2 |     -3 |      5 |    1 |           -1
   3 |     -2 |      4 |    1 |           -1
   4 |      1 |      4 |    1 |           -1
   5 |      4 |      8 |    1 |           -1
   6 |      4 |     10 |    1 |           -1
   7 |      5 |      9 |    1 |           -1
   8 |      5 |     11 |    1 |           -1
   9 |      6 |      7 |    1 |           -1
  10 |      7 |      8 |    1 |           -1
  11 |      7 |     10 |    1 |           -1
  12 |      8 |      9 |    1 |           -1
  13 |      8 |     11 |    1 |           -1
  14 |      9 |     15 |    1 |           -1
  15 |     10 |     12 |    1 |           -1
  16 |     10 |     14 |    1 |           -1
  17 |     11 |     13 |    1 |           -1
  18 |     12 |     13 |    1 |           -1
  19 |     16 |     15 |    1 |           -1
(19 rows)

Parameters

Column	Type	Description
edges_sql	TEXT	SQL query as described above.
directed	BOOLEAN	When true the graph is considered as Directed. When false the graph is considered as Undirected.

Inner query

Column	Type	Default	Description
id	ANY-INTEGER		Identifier of the edge.
source	ANY-INTEGER		Identifier of the first end point vertex of the edge.
target	ANY-INTEGER		Identifier of the second end point vertex of the edge.
cost	ANY-NUMERICAL		Weight of the edge (source, target) When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost	ANY-NUMERICAL	-1	Weight of the edge (target, source), When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

Where:

ANY-INTEGER

SMALLINT, INTEGER, BIGINT

ANY-NUMERICAL

SMALLINT, INTEGER, BIGINT, REAL, FLOAT

Result Columns

RETURNS SETOF (seq, source, target, cost, reverse_cost)

Column	Type	Description
seq	INTEGER	Sequential value starting from 1.
source	BIGINT	Identifier of the source vertex of the current edge id. When negative: the source is the reverse edge in the original graph.
target	BIGINT	Identifier of the target vertex of the current edge id. When negative: the target is the reverse edge in the original graph.
cost	FLOAT	Weight of the edge (source, target). When negative: edge (source, target) does not exist, therefore it’s not part of the graph.
reverse_cost	FLOAT	Weight of the edge (target, source). When negative: edge (target, source) does not exist, therefore it’s not part of the graph.

See Also

• https://en.wikipedia.org/wiki/Line_graph

• The queries use the Sample Data network.

Indices and tables

• Index

• Search Page