pgr_kruskalDD¶
pgr_kruskalDD
— Catchament nodes using Kruskal’s algorithm.
Availability
Version 3.0.0
New Official function
Support
Description¶
Using Kruskal’s algorithm, extracts the nodes that have aggregate costs less than
or equal to the value Distance
from a root vertex (or vertices) within
the calculated minimum spanning tree.
The main Characteristics are:
It’s implementation is only on undirected graph.
Process is done only on edges with positive costs.
The total weight of all the edges in the tree or forest is minimized.
When the graph is connected
The resulting edges make up a tree
When the graph is not connected,
Finds a minimum spanning tree for each connected component.
The resulting edges make up a forest.
Kruskal’s running time: \(O(E * log E)\)
Returned tree nodes from a root vertex are on Depth First Search order.
Depth First Search running time: \(O(E + V)\)
Signatures¶
pgr_kruskalDD(edges_sql, root_vid, distance)
pgr_kruskalDD(edges_sql, root_vids, distance)
RETURNS SET OF (seq, depth, start_vid, node, edge, cost, agg_cost)
Single vertex¶
pgr_kruskalDD(edges_sql, root_vid, distance)
RETURNS SET OF (seq, depth, start_vid, node, edge, cost, agg_cost)
 Example
The Minimum Spanning Tree starting on vertex \(2\) with \(agg\_cost <= 3.5\)
SELECT * FROM pgr_kruskalDD(
'SELECT id, source, target, cost, reverse_cost FROM edge_table ORDER BY id',
2, 3.5
);
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  3  2  9  16  1  3
(5 rows)
Multiple vertices¶
pgr_kruskalDD(edges_sql, root_vids, distance)
RETURNS SET OF (seq, depth, start_vid, node, edge, cost, agg_cost)
 Example
The Minimum Spanning Tree starting on vertices \(\{13, 2\}\) with \(agg\_cost <= 3.5\);
SELECT * FROM pgr_kruskalDD(
'SELECT id, source, target, cost, reverse_cost FROM edge_table ORDER BY id',
ARRAY[13,2],
3.5
);
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  3  2  9  16  1  3
6  0  13  13  1  0  0
7  1  13  10  14  1  1
8  2  13  5  10  1  2
9  3  13  8  7  1  3
10  2  13  11  12  1  2
11  3  13  6  11  1  3
12  3  13  12  13  1  3
(12 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.

Distance 

Upper limit for the inclusion of the node in the result.

Where:
 ANYINTEGER
SMALLINT, INTEGER, BIGINT
 ANYNUMERIC
SMALLINT, INTEGER, BIGINT, REAL, FLOAT, NUMERIC
Inner query¶
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 

Weight of the edge (source, target)


reverse_cost 

1 
Weight of the edge (target, source),

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 