Make graph components accessible

[rdnfn]

Description: for the UI it would be great to have the following method/function, either as part of GeoGraph or as a standalone function:

def get_graph_components(graph: nx.Graph()) -> gpd.GeoDataFrame():
    """Return a GeoDataFrame with graph components.

    This method takes an nx.Graph and determines the individual disconnected graph
    components that make up the graph. Each row of the returned GeoDataFrame 
    corresponds to a graph component, with entries in column 'geometry' being the union
    of all individual polygons making up a component.

    This method allows for the UI to visualise components and output their number as 
    a metric.

    More info on the definition of graph components can be found here:
    https://en.wikipedia.org/wiki/Component_(graph_theory)

    Args:
        graph (nx.Graph): nx.Graph of a GeoGraph
    """

Using the returned GeoDataFrame, the UI can then color code the components and output their number as a metric.

[rdnfn]

@herbiebradley: do you know if NetworkX already has some component functionality built-in?

[herbiebradley]

This should be fairly easy to do using https://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.components.connected_components.html

That will return a list of node indices which make up the components, then dataframes have plenty of ways of selecting only a limited number of rows, so it should be easy to just slice the main graph dataframe and return only the relevant rows.

[rdnfn]

Brilliant, that looks very promising!

[herbiebradley]

Closed by #31