Unable to import undirected graph from EdgeList file in igraph-python
Question: I am using the igraph-python's `Graph.Read_Ncol` function. Below is my code
for reading the data.

    
    
    def loadData(filename):
        data = None
        data = ig.Graph.Read_Ncol(filename, directed=False)
        return data
    

I am using this dataset from SNAP group: <https://snap.stanford.edu/data/ca-
GrQc.html> As mentioned the dataset has 14496 edges and 5242 nodes.

However when I do `data.summary()` on my graph I get the following output.

    
    
    >>> data.summary()
    'IGRAPH UN-- 5242 28980 -- \n+ attr: name (v)'
    

Even when I am doing `data.to_undirected()` and trying `data.summary()` again
I am getting the same result as above.

    
    
    >>> data.to_undirected()
    >>> data.summary()
    'IGRAPH UN-- 5242 28980 -- \n+ attr: name (v)'
    

When I am loading the graph using the SNAP library in an undirected fashion
then I am getting the correct output.

    
    
    def loadData(filename):
        data = None
        data = snap.LoadEdgeList(snap.PUNGraph,filename,0,1)
    
        return data
    

What am I doing wrong? Or is there an issue with the igraph API?


Answer: Most of the edges appear twice in your network, and igraphs adds them as
multiple edges. Call `simplify()` on the graph to remove these multiple edges.
<http://igraph.org/python/doc/igraph.GraphBase-class.html#simplify>

