Can import edgelist to igraph python
Question: I have a list of twitter followers in text file that I want to import to
iGraph.

Here's the sample of my list

    
    
    393795446 18215973
    393795446 582203919
    393795446 190709835
    393795446 1093090866
    393795446 157780872
    393795446 1580109739
    393795446 3301748909
    393795446 1536791610
    393795446 106170345
    393795446 9409752
    

And this is how I import it

    
    
    from igraph import *
    twitter_igraph = Graph.Read_Edgelist('twitter_edgelist.txt', directed=True)
    

But I get this error.

    
    
    ---------------------------------------------------------------------------
    InternalError                             Traceback (most recent call last)
    <ipython-input-10-d808f2237fa8> in <module>()
    ----> 1 twitter_igraph = Graph.Read_Edgelist('twitter_edgelist.txt', directed=True)
    
    InternalError: Error at type_indexededgelist.c:369: cannot add negative number of vertices, Invalid value
    

I'm not sure why it's saying something about negative number. I check the file
and it doesn't have any negative number or id.


Answer: You need to use `graph.Read_Ncol` for this type of file format. Why your file
doesn't conform to a typical "edgelist" format is beyond me. I've wondered
this myself many times. I should also mention that I grabbed the answer from
[here](http://stackoverflow.com/questions/14471473/format-for-importing-
edgelist-into-igraph-in-python). Tamàs seems to be the main igraph guy around
here. I'm sure he can give a more detailed reason as to why you need to use
`Ncol` as opposed to `Edgelist`.

This works for me.

    
    
    from igraph import *
    twitter_igraph = Graph.Read_Ncol('twitter_edgelist.txt', directed=True)
    

* * *

**Personal Plug**

This is a great example of where igraph's documentation could be improved.

For example: The only accompanying text with [graph.Read_Edgelist()
doc](http://igraph.org/python/doc/igraph.GraphBase-class.html#Read_Edgelist)
says...

> Reads an edge list from a file and creates a graph based on it. Please note
> that the vertex indices are zero-based.

This doesn't really tell me anything when obviously there are nuances with how
the file needs to be formatted. Saying what format this function expects the
file to be in would save a lot of people their sanity.

