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:file: This file is part of the pgRouting project.
:copyright: Copyright (c) 2016-2026 pgRouting developers
:license: Creative Commons Attribution-Share Alike 3.0 https://creativecommons.org/licenses/by-sa/3.0
.. index::
single: Components Family ; pgr_connectedComponents
single: connectedComponents
|
``pgr_connectedComponents``
===============================================================================
``pgr_connectedComponents`` — Connected components of an undirected graph using
a DFS-based approach.
.. rubric:: Availability
* Version 3.0.0
* Result columns change:
* ``n_seq`` is removed
* ``seq`` changed type to ``BIGINT``
* Function promoted to official.
* Version 2.5.0
* New experimental function.
Description
-------------------------------------------------------------------------------
A connected component of an undirected graph is a set of vertices that are all
reachable
from each other.
**The main characteristics are:**
- Works for **undirected** graphs.
- Components are described by vertices
- The returned values are ordered:
- ``component`` ascending
- ``node`` ascending
- Running time: :math:`O(V + E)`
|Boost| Boost Graph Inside
Signatures
-------------------------------------------------------------------------------
.. admonition:: \ \
:class: signatures
| pgr_connectedComponents(`Edges SQL`_)
| Returns set of |result-component-V|
| OR EMPTY SET
:Example: The connected components of the graph
.. literalinclude:: connectedComponents.queries
:start-after: -- q1
:end-before: -- q2
.. figure:: /images/cc_sampledata.png
:scale: 25%
Parameters
-------------------------------------------------------------------------------
.. include:: pgRouting-concepts.rst
:start-after: only_edge_param_start
:end-before: only_edge_param_end
Inner Queries
-------------------------------------------------------------------------------
Edges SQL
...............................................................................
.. include:: pgRouting-concepts.rst
:start-after: basic_edges_sql_start
:end-before: basic_edges_sql_end
Result columns
-------------------------------------------------------------------------------
.. return_componentsV_start
Returns set of |result-component-V|
.. list-table::
:width: 81
:widths: auto
:header-rows: 1
* - Column
- Type
- Description
* - ``seq``
- ``BIGINT``
- Sequential value starting from **1**.
* - ``component``
- ``BIGINT``
- Component identifier.
* Has the value of the minimum node identifier in the component.
* - ``node``
- ``BIGINT``
- Identifier of the vertex that belongs to the ``component``.
.. return_componentsV_end
Additional Examples
-------------------------------------------------------------------------------
Connecting disconnected components
...............................................................................
.. include:: pgRouting-concepts.rst
:start-after: connecting_graph_start
:end-before: connecting_graph_end
See Also
-------------------------------------------------------------------------------
* :doc:`components-family`
* :doc:`sampledata`
* `Boost: Connected components
<https://www.boost.org/libs/graph/doc/connected_components.html>`__
* wikipedia: `Connected component
<https://en.wikipedia.org/wiki/Connected_component_(graph_theory)>`__
.. rubric:: Indices and tables
* :ref:`genindex`
* :ref:`search`
|
