pgr_strongComponents  pgRouting Manual (3.4)
pgr_strongComponents
pgr_strongComponents
 Strongly connected components of a directed graph
using Tarjan’s algorithm based on DFS.
Availability

Version 3.0.0

Return columns change:

n_seq
is removed 
seq
changed type toBIGINT


Official function


Version 2.5.0

New experimental function

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:

Works for directed graphs.

Components are described by vertices identifiers.

The returned values are ordered:

component
ascending 
node
ascending


Running time: \(O(V + E)\)
Signatures
 Example :

The strong components of the graph
SELECT * FROM pgr_strongComponents(
'SELECT id, source, target, cost, reverse_cost FROM edges'
);
seq component node
++
1 1 1
2 1 3
3 1 5
4 1 6
5 1 7
6 1 8
7 1 9
8 1 10
9 1 11
10 1 12
11 1 15
12 1 16
13 1 17
14 2 2
15 2 4
16 13 13
17 13 14
(17 rows)
Parameters
Parameter 
Type 
Description 


Edges SQL as described below. 
Inner Queries
Edges SQL
Column 
Type 
Default 
Description 


ANYINTEGER 
Identifier of the edge. 


ANYINTEGER 
Identifier of the first end point vertex of the edge. 


ANYINTEGER 
Identifier of the second end point vertex of the edge. 


ANYNUMERICAL 
Weight of the edge (



ANYNUMERICAL 
1 
Weight of the edge (

Where:
 ANYINTEGER :

SMALLINT
,INTEGER
,BIGINT
 ANYNUMERICAL :

SMALLINT
,INTEGER
,BIGINT
,REAL
,FLOAT
Result Columns
Returns set of
(seq,
component,
node)
Column 
Type 
Description 



Sequential value starting from 1 . 


Component identifier.



Identifier of the vertex that belongs to the

See Also

The queries use the Sample Data network.

Boost: Strong components

wikipedia: Strongly connected component
Indices and tables