pgr_dijkstraCost

pgr_dijkstraCost

Using Dijkstra algorithm implemented by Boost.Graph, and extract only the aggregate cost of the shortest path(s) found, for the combination of vertices given.

images/boost-inside.jpeg

Boost Graph Inside

Availability

  • Version 3.1.0

    • New Proposed functions:

      • pgr_dijkstraCost(combinations)

  • Version 2.2.0

    • New Official function

Description

The pgr_dijkstraCost algorithm, is a good choice to calculate the sum of the costs of the shortest path for a subset of pairs of nodes of the graph. We make use of the Boost’s implementation of dijkstra which runs in \(O(V \log V + E)\) time.

The main characteristics are:
  • It does not return a path.

  • Returns the sum of the costs of the shortest path for pair combination of nodes in the graph.

  • Process is done only on edges with positive costs.

  • Values are returned when there is a path.

    • The returned values are in the form of a set of (start_vid, end_vid, agg_cost) .

    • When the starting vertex and ending vertex are the same, there is no path.

      • The agg_cost int the non included values (v, v) is 0

    • When the starting vertex and ending vertex are the different and there is no path.

      • The agg_cost in the non included values (u, v) is \(\infty\)

  • Let be the case the values returned are stored in a table, so the unique index would be the pair: (start_vid, end_vid) .

  • For undirected graphs, the results are symmetric.

    • The agg_cost of (u, v) is the same as for (v, u) .

  • Any duplicated value in the start_vids or end_vids is ignored.

  • The returned values are ordered:

    • start_vid ascending

    • end_vid ascending

  • Running time: \(O( start\_vids * (V \log V + E))\)

Signatures

Summary

pgr_dijkstraCost(edges_sql, from_vid,  to_vid  [, directed])
pgr_dijkstraCost(edges_sql, from_vid,  to_vids [, directed])
pgr_dijkstraCost(edges_sql, from_vids, to_vid  [, directed])
pgr_dijkstraCost(edges_sql, from_vids, to_vids [, directed])
pgr_dijkstraCost(edges_sql, combinations_sql   [, directed]) -- Proposed on v3.1
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET

Using defaults

pgr_dijkstraCost(edges_sql, from_vid,  to_vid)
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
Example :

From vertex \(2\) to vertex \(3\) on a directed graph

SELECT * FROM pgr_dijkstraCost(
    'select id, source, target, cost, reverse_cost from edge_table',
    2, 3);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         2        3         5
(1 row)

One to One

pgr_dijkstraCost(edges_sql, from_vid,  to_vid  [, directed])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
Example :

From vertex \(2\) to vertex \(3\) on an undirected graph

SELECT * FROM pgr_dijkstraCost(
    'select id, source, target, cost, reverse_cost from edge_table',
    2, 3, false);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         2        3         1
(1 row)

One to Many

pgr_dijkstraCost(edges_sql, from_vid,  to_vids [, directed])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
Example :

From vertex \(2\) to vertices \(\{3, 11\}\) on a directed graph

SELECT * FROM pgr_dijkstraCost(
    'select id, source, target, cost, reverse_cost from edge_table',
    2, ARRAY[3, 11]);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         2        3         5
         2       11         3
(2 rows)

Many to One

pgr_dijkstraCost(edges_sql, from_vids, to_vid  [, directed])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
Example :

From vertices \(\{2, 7\}\) to vertex \(3\) on a directed graph

SELECT * FROM pgr_dijkstraCost(
    'select id, source, target, cost, reverse_cost from edge_table',
    ARRAY[2, 7], 3);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         2        3         5
         7        3         6
(2 rows)

Many to Many

pgr_dijkstraCost(edges_sql, from_vids, to_vids [, directed])
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
Example :

From vertices \(\{2, 7\}\) to vertices \(\{3, 11\}\) on a directed graph

SELECT * FROM pgr_dijkstraCost(
    'select id, source, target, cost, reverse_cost from edge_table',
    ARRAY[2, 7], ARRAY[3, 11]);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         2        3         5
         2       11         3
         7        3         6
         7       11         4
(4 rows)

Combinations

pgr_dijkstraCost(TEXT edges_sql, TEXT combination_sql, BOOLEAN directed:=true);
RETURNS SET OF (start_vid, end_vid, agg_cost)
OR EMPTY SET
Example :

Using a combinations table on an undirected graph

SELECT * FROM pgr_dijkstraCost(
    'SELECT id, source, target, cost, reverse_cost FROM edge_table',
    'SELECT source, target FROM combinations_table',
    FALSE
);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         1        2         1
         1        4         3
         2        1         1
         2        4         2
(4 rows)

Parameters

Parameter

Type

Default

Description

Edges SQL

TEXT

Edges query as described below

Combinations SQL

TEXT

Combinations query as described below

start_vid

BIGINT

Identifier of the starting vertex of the path.

start_vids

ARRAY[BIGINT]

Array of identifiers of starting vertices.

end_vid

BIGINT

Identifier of the ending vertex of the path.

end_vids

ARRAY[BIGINT]

Array of identifiers of ending vertices.

directed

BOOLEAN

true

  • When true Graph is considered Directed

  • When false the graph is considered as Undirected .

Inner query

Edges 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

Combinations query

Column

Type

Default

Description

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.

Where:

ANY-INTEGER :

SMALLINT, INTEGER, BIGINT

Return Columns

Returns SET OF (start_vid, end_vid, agg_cost)

Column

Type

Description

start_vid

BIGINT

Identifier of the starting vertex.

end_vid

BIGINT

Identifier of the ending vertex.

agg_cost

FLOAT

Aggregate cost from start_vid to end_vid .

Additional Examples

Example 1 :

Demonstration of repeated values are ignored, and result is sorted.

SELECT * FROM pgr_dijkstraCost(
        'select id, source, target, cost, reverse_cost from edge_table',
            ARRAY[5, 3, 4, 3, 3, 4], ARRAY[3, 5, 3, 4]);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         3        4         3
         3        5         2
         4        3         1
         4        5         3
         5        3         4
         5        4         3
(6 rows)

Example 2 :

Making start_vids the same as end_vids

SELECT * FROM pgr_dijkstraCost(
        'select id, source, target, cost, reverse_cost from edge_table',
            ARRAY[5, 3, 4], ARRAY[5, 3, 4]);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         3        4         3
         3        5         2
         4        3         1
         4        5         3
         5        3         4
         5        4         3
(6 rows)

Example 3 :

Four manually assigned (source, target) vertex combinations

SELECT * FROM pgr_dijkstraCost(
    'SELECT id, source, target, cost FROM edge_table',
    'SELECT * FROM (VALUES (2, 3), (2, 5), (11, 3), (11, 5)) AS combinations (source, target)',
    FALSE
);
 start_vid  end_vid  agg_cost
-----------+---------+----------
         2        3         3
         2        5         1
        11        3         2
        11        5         2
(4 rows)

See Also

Indices and tables