Add delimiter keyword to write_edgelist

[macks22]

Currently spaces are used. It would be useful to be able to write a standard csv or tsv file, for instance.

[gaborcsardi]

Sounds reasonable. But then maybe for reading as well.

[macks22]

Indeed. This could also be implied from the extension like the general write/Read methods do. For instance, csv/tsv would be implied comma/tab, and txt might be the space as it currently is. A more general delimiter-separated-value could be ext .dsv and require a format specified. Or several other non-standard options could be defined to accommodate standard delimiters such as .ssv for semi-colons, .psv for pipes, etc. This may get to be too much though, so just sticking with either a delimiter keyword or standard options will probably be simpler.

When reading, you could also imply the delimiter if using a standard header, such as (src,target) for each edgelist file.

[iosonofabio]

I can't seem to find the function write_edgelist in the C library. Maybe R specific? If so should we move the issue to that repo?

[szhorvat]

@iosonofabio I believe this refers to igraph_write_graph_edgelist and igraph_read_graph_edgelist.

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[carissableker]

I would appreciate if the same option could be added to igraph_write_graph_ncol as well.

[sajaddp]

Hi, Is there a plan for this issue after six years?

[iosonofabio]

haha @sajaddp there is a plan! It's a simple fix, so feel free to make a PR for it. Otherwise I'll try to find some time in the next days and it'll make it for the next release