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 removedseq
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
ascendingnode
ascending
Running time: \(O(V + E)\)
Signatures¶
(seq, component, node)
 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