graphio.h File Reference

Description

Methods for reading and writing graphs to disk.

For an introduction to the file formats supported by STAG, see Graph File Formats.

Functions
stag::Graph	stag::load_edgelist (std::string &filename)
void	stag::save_edgelist (stag::Graph &graph, std::string &filename)
stag::Graph	stag::load_adjacencylist (std::string &filename)
void	stag::save_adjacencylist (stag::Graph &graph, std::string &filename)
void	stag::edgelist_to_adjacencylist (std::string &edgelist_fname, std::string &adjacencylist_fname)
void	stag::adjacencylist_to_edgelist (std::string &adjacencylist_fname, std::string &edgelist_fname)

Function Documentation

load_edgelist()

stag::Graph stag::load_edgelist

(

std::string &

filename

)

Load a graph from an edgelist file.

We define an edgelist file in the following way.

• Any lines beginning with '#' or '//' are ignored
• Any blank lines are ignored

• All other lines are of one of the formats

  • <u>, <v>, <weight>
  • <u>, <v>
  • <u> <v> <weight>
  • <u> <v>

  where <u> and <v> can be parsed as integers, and <weight> can be parsed as a double. If the weight is omitted, it is taken to be 1.

Here is an example edgelist file.

# This line is ignored
0, 1, 0.5
1, 2, 1
2, 0, 0.5

Parameters

filename

the name of the edgelist file to be loaded

Returns

stag::Graph object

Exceptions

std::runtime_error

if the file doesn't exist or cannot be parsed as an edgelist

save_edgelist()

void stag::save_edgelist	(	stag::Graph &	graph,
		std::string &	filename
	)

Save the given graph as an edgelist file.

Parameters

graph	the graph object to be saved
filename	the name of the file to save the edgelist data to

load_adjacencylist()

stag::Graph stag::load_adjacencylist

(

std::string &

filename

)

Load a graph from an adjacencylist file.

The adjacency list file format is defined in the following way.

• Any lines beginning with # or // are ignored
• Any blank lines are ignored
• All other lines have the format <node_id>: <list of neighbours>, where <node_id> is an integer and <list of neighbours> is either a space-separated list of integers or a space-separated list of <id>:<weight> where <id> gives the id of the neighbour and <weight> is the weight of the edge.
• The <node IDs> of each line must be sorted in increasing order.
• The graph should have no self-loops.

Here is an example adjacencylist file.

# This line is ignored
0: 1 2
1: 0 2 3
2: 0 1
3: 1

The following example includes weighted edges.

# This line is ignored
0: 1:0.5 2:0.5
1: 0:0.5 2:1
2: 0:0.5 1:1

Note that this method loads the entire graph into memory. For large graphs, the stag::AdjacencyListLocalGraph object can be used to access the graph in a 'local' way without reading the entire graph into memory.

Parameters

filename

the name of the adjacency list file to be loaded

Returns

stag::Graph object

Exceptions

std::runtime_error

if the file doesn't exist or cannot be parsed as an adjacency list

save_adjacencylist()

void stag::save_adjacencylist	(	stag::Graph &	graph,
		std::string &	filename
	)

Save the given graph as an adjacencylist file.

Parameters

graph	the graph object to be saved
filename	the name of the file to save the adjacencylist data to

edgelist_to_adjacencylist()

void stag::edgelist_to_adjacencylist	(	std::string &	edgelist_fname,
		std::string &	adjacencylist_fname
	)

Convert an edgelist file to an adjacency list.

Parameters

edgelist_fname	the name of the file containing the edgelist.
adjacencylist_fname	the name of the file to write the adjacencylist.

adjacencylist_to_edgelist()

void stag::adjacencylist_to_edgelist	(	std::string &	adjacencylist_fname,
		std::string &	edgelist_fname
	)

Convert an adjacency list file to an edgelist.

Parameters

adjacencylist_fname	the name of the file containing the adjacency list.
edgelist_fname	the name of the file to write the edgelist.