igraph.EdgeSeq

Class representing a sequence of edges in the graph.

This class is most easily accessed by the es field of the Graph object, which returns an ordered sequence of all edges in the graph. The edge sequence can be refined by invoking the EdgeSeq.select() method. EdgeSeq.select() can also be accessed by simply calling the EdgeSeq object.

An alternative way to create an edge sequence referring to a given graph is to use the constructor directly:

>>> g = Graph.Full(3)
>>> es = EdgeSeq(g)
>>> restricted_es = EdgeSeq(g, [0, 1])

The individual edges can be accessed by indexing the edge sequence object. It can be used as an iterable as well, or even in a list comprehension:

>>> g=Graph.Full(3)
>>> for e in g.es:
...   print(e.tuple)
...
(0, 1)
(0, 2)
(1, 2)
>>> [max(e.tuple) for e in g.es]
[1, 2, 2]

The edge sequence can also be used as a dictionary where the keys are the attribute names. The values corresponding to the keys are the values of the given attribute of every edge in the graph:

>>> g=Graph.Full(3)
>>> for idx, e in enumerate(g.es):
...   e["weight"] = idx*(idx+1)
...
>>> g.es["weight"]
[0, 2, 6]
>>> g.es["weight"] = range(3)
>>> g.es["weight"]
[0, 1, 2]

If you specify a sequence that is shorter than the number of edges in the EdgeSeq, the sequence is reused:

>>> g = Graph.Tree(7, 2)
>>> g.es["color"] = ["red", "green"]
>>> g.es["color"]
['red', 'green', 'red', 'green', 'red', 'green']

You can even pass a single string or integer, it will be considered as a sequence of length 1:

>>> g.es["color"] = "red"
>>> g.es["color"]
['red', 'red', 'red', 'red', 'red', 'red']

Some methods of the edge sequences are simply proxy methods to the corresponding methods in the Graph object. One such example is EdgeSeq.is_multiple():

>>> g=Graph(3, [(0,1), (1,0), (1,2)])
>>> g.es.is_multiple()
[False, True, False]
>>> g.es.is_multiple() == g.is_multiple()
True