pgr_strongComponents

pgr_strongComponents — Strongly connected components of a directed graph using Tarjan’s algorithm based on DFS.

_images/boost-inside.jpeg

Boost Graph Inside

Availability

  • Version 3.0.0

    • Return columns change:

      • n_seq is removed

      • seq changed type to BIGINT

    • Official function

  • Version 2.5.0

    • New experimental function

Support

  • Supported versions: current(3.0)

  • Unsupported versions: 2.6 2.5

Description

A strongly connected component of a directed graph is a set of vertices that are all reachable from each other.

The main characteristics are:

  • The signature is for a directed graph.

  • Components are described by vertices

  • The returned values are ordered:

    • component ascending

    • node ascending

  • Running time: \(O(V + E)\)

Signatures

pgr_strongComponents(Edges SQL)

RETURNS SET OF (seq, component, node)
OR EMPTY SET
Example

The strong components of the graph

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

Parameters

Parameter

Type

Default

Description

Edges SQL

TEXT

Inner query as described below.

Inner query

edges SQL

an SQL query of a directed graph, which should return a set of rows with the following columns:

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 set of (seq, component, node)

Column

Type

Description

seq

BIGINT

Sequential value starting from 1.

component

BIGINT

Component identifier. It is equal to the minimum node identifier in the component.

node

BIGINT

Identifier of the vertex that belongs to component.

See Also

Indices and tables