add from_igraph and to_pygsp methods

graphtools/__init__.py

@@ -1,2 +1,2 @@
-from .api import Graph
+from .api import Graph, from_igraph
 from .version import __version__

graphtools/api.py

@@ -1,6 +1,7 @@
 import numpy as np
 import warnings
 import tasklogger
+from scipy import sparse
 
 from . import base
 from . import graphs
@@ -222,3 +223,10 @@ def Graph(data,
                    for key, value in params.items()
                    if key != "data"])))
     return Graph(**params)
+
+
+def from_igraph(G, **kwargs):
+    if 'precomputed' in kwargs and kwargs['precomputed'] != 'adjacency':
+        raise ValueError("Cannot build graph from igraph with precomputed={}. "
+                         "Use 'adjacency' instead.".format(kwargs['precomputed']))
+    return Graph(sparse.coo_matrix(G.get_adjacency().data), precomputed='adjacency', **kwargs)

graphtools/base.py

@@ -27,6 +27,7 @@
                     elementwise_maximum,
                     set_diagonal)
 
+
 class Base(object):
     """Class that deals with key-word arguments but is otherwise
     just an object.
@@ -534,6 +535,10 @@ def build_kernel(self):
         """
         raise NotImplementedError
 
+    def to_pygsp(self):
+        from . import api
+        return api.Graph(self.K, precomputed="affinity", use_pygsp=True)
+
 
 class PyGSPGraph(with_metaclass(abc.ABCMeta, pygsp.graphs.Graph, Base)):
     """Interface between BaseGraph and PyGSP.

setup.py

@@ -15,7 +15,8 @@
     'nose2',
     'pandas',
     'coverage',
-    'coveralls'
+    'coveralls',
+    'python-igraph'
 ]
 
 if sys.version_info[0] == 3:

test/test_api.py

@@ -4,8 +4,30 @@
     build_graph,
     raises,
 )
+import igraph
+import numpy as np
+import graphtools
 
 
+def test_from_igraph():
+    n = 100
+    m = 500
+    K = np.zeros((n, n))
+    for _ in range(m):
+        e = np.random.choice(n, 2, replace=False)
+        K[e[0], e[1]] = K[e[1], e[0]] = 1
+    g = igraph.Graph.Adjacency(K.tolist())
+    G = graphtools.from_igraph(g)
+    G2 = graphtools.Graph(K, precomputed='adjacency')
+    assert np.all(G.K == G2.K)
+
+
+def test_to_pygsp():
+    G = build_graph(data)
+    G2 = G.to_pygsp()
+    assert isinstance(G2, graphtools.graphs.PyGSPGraph)
+    assert np.all(G2.K == G.K)
+
 #####################################################
 # Check parameters
 #####################################################