[igraph] reading edgelist with weight

[Ross KK Leung]

When I pass a file with only 3 columns, with the last one as weight. And
then I encounter this error and I'm unable to identify documentation for it.


Parse error in NCOL file, line 1 (syntax error, unexpected ALNUM, expecting
NEWLINE), Parse error

The weight is very important to be read in this stage because I find that
graph.neighborhood output list will not necessarily follow the same order as
in the input file. Therefore "adding back" may miss some of the edges and it
is also inefficient to work for 100,000+ edges.