pgr_depthFirstSearch  Proposed  pgRouting Manual (3.3)
pgr_depthFirstSearch  Proposed
pgr_depthFirstSearch
 Returns a depth first search traversal of the graph.
The graph can be directed or undirected.
Warning
Proposed functions for next mayor release.

They are not officially in the current release.

They will likely officially be part of the next mayor release:

The functions make use of ANYINTEGER and ANYNUMERICAL

Name might not change. (But still can)

Signature might not change. (But still can)

Functionality might not change. (But still can)

pgTap tests have being done. But might need more.

Documentation might need refinement.

Availability

Version 3.3.0

Promoted to proposed function


Version 3.2.0

New experimental function

Description
Depth First Search algorithm is a traversal algorithm which starts from a root vertex, goes as deep as possible, and backtracks once a vertex is reached with no adjacent vertices or with all visited adjacent vertices. The traversal continues until all the vertices reachable from the root vertex are visited.
The main Characteristics are:

The implementation works for both directed and undirected graphs.

Provides the Depth First Search traversal order from a root vertex or from a set of root vertices.

An optional nonnegative maximum depth parameter to limit the results up to a particular depth.

For optimization purposes, any duplicated values in the Root vids are ignored.

It does not produce the shortest path from a root vertex to a target vertex.

The aggregate cost of traversal is not guaranteed to be minimal.

The returned values are ordered in ascending order of start_vid .

Depth First Search Running time: \(O(E + V)\)
Signatures
Summary
pgr_depthFirstSearch(Edges SQL, Root vid [, directed] [, max_depth])
pgr_depthFirstSearch(Edges SQL, Root vids [, directed] [, max_depth])
RETURNS SET OF (seq, depth, start_vid, node, edge, cost, agg_cost)
Using defaults
 Example :

From root vertex \(2\) on a directed graph
SELECT * FROM pgr_depthFirstSearch(
'SELECT id, source, target, cost, reverse_cost FROM edge_table
ORDER BY id',
2
);
seq depth start_vid node edge cost agg_cost
++++++
1 0 2 2 1 0 0
2 1 2 1 1 1 1
3 1 2 5 4 1 1
4 2 2 8 7 1 2
5 3 2 7 6 1 3
6 2 2 6 8 1 2
7 3 2 9 9 1 3
8 4 2 12 15 1 4
9 4 2 4 16 1 4
10 5 2 3 3 1 5
11 3 2 11 11 1 3
12 2 2 10 10 1 2
13 3 2 13 14 1 3
(13 rows)
Single vertex
pgr_depthFirstSearch(Edges SQL, Root vid [, directed] [, max_depth])
RETURNS SET OF (seq, depth, start_vid, node, edge, cost, agg_cost)
 Example :

From root vertex \(2\) on an undirected graph, with \(depth <= 2\)
SELECT * FROM pgr_depthFirstSearch(
'SELECT id, source, target, cost, reverse_cost FROM edge_table
ORDER BY id',
2, directed => false, max_depth => 2
);
seq depth start_vid node edge cost agg_cost
++++++
1 0 2 2 1 0 0
2 1 2 1 1 1 1
3 1 2 3 2 1 1
4 2 2 4 3 1 2
5 2 2 6 5 1 2
6 1 2 5 4 1 1
7 2 2 8 7 1 2
8 2 2 10 10 1 2
(8 rows)
Multiple vertices
pgr_depthFirstSearch(Edges SQL, Root vids [, directed] [, max_depth])
RETURNS SET OF (seq, depth, start_vid, node, edge, cost, agg_cost)
 Example :

From root vertices \(\{11, 2\}\) on an undirected graph with \(depth <= 2\)
SELECT * FROM pgr_depthFirstSearch(
'SELECT id, source, target, cost, reverse_cost FROM edge_table
ORDER BY id',
ARRAY[11, 2], directed => false, max_depth => 2
);
seq depth start_vid node edge cost agg_cost
++++++
1 0 2 2 1 0 0
2 1 2 1 1 1 1
3 1 2 3 2 1 1
4 2 2 4 3 1 2
5 2 2 6 5 1 2
6 1 2 5 4 1 1
7 2 2 8 7 1 2
8 2 2 10 10 1 2
9 0 11 11 1 0 0
10 1 11 6 11 1 1
11 2 11 3 5 1 2
12 2 11 5 8 1 2
13 2 11 9 9 1 2
14 1 11 10 12 1 1
15 2 11 13 14 1 2
16 1 11 12 13 1 1
(16 rows)
Parameters
Parameter 
Type 
Description 

Edges SQL 

SQL query described in Inner query . 
Root vid 

Identifier of the root vertex of the tree.

Root vids 

Array of identifiers of the root vertices.

Optional Parameters
Parameter 
Type 
Default 
Description 

directed 



max_depth 

\(9223372036854775807\) 
Upper limit for the depth of traversal

Inner query
Edges SQL
Column 
Type 
Default 
Description 

id 

Identifier of the edge. 

source 

Identifier of the first end point vertex of the edge. 

target 

Identifier of the second end point vertex of the edge. 

cost 



reverse_cost 

1 

Where:
 ANYINTEGER :

SMALLINT, INTEGER, BIGINT
 ANYNUMERICAL :

SMALLINT, INTEGER, BIGINT, REAL, FLOAT
Result Columns
Returns SET OF
(seq,
depth,
start_vid,
node,
edge,
cost,
agg_cost)
Column 
Type 
Description 

seq 

Sequential value starting from \(1\) . 
depth 

Depth of the

start_vid 

Identifier of the root vertex.

node 

Identifier of

edge 

Identifier of the

cost 

Cost to traverse

agg_cost 

Aggregate cost from

Additional Examples
The examples of this section are based on the Sample Data network.
Example: No internal ordering on traversal
In the following query, the inner query of the example: "Using defaults" is modified so that the data is entered into the algorithm is given in the reverse ordering of the id.
SELECT * FROM pgr_depthFirstSearch(
'SELECT id, source, target, cost, reverse_cost FROM edge_table
ORDER BY id DESC',
2
);
seq depth start_vid node edge cost agg_cost
++++++
1 0 2 2 1 0 0
2 1 2 5 4 1 1
3 2 2 10 10 1 2
4 3 2 13 14 1 3
5 3 2 11 12 1 3
6 4 2 12 13 1 4
7 5 2 9 15 1 5
8 6 2 4 16 1 6
9 7 2 3 3 1 7
10 8 2 6 5 1 8
11 2 2 8 7 1 2
12 3 2 7 6 1 3
13 1 2 1 1 1 1
(13 rows)
The resulting traversal is different.
The left image shows the result with ascending order of ids and the right image shows with descending order of ids:
See Also

The queries use the Sample Data network.
Indices and tables