Add arrows to edges for directed network graphs

[cacti77]

I see an example of a network graph at http://holoviews.org/gallery/demos/bokeh/network_graph.html but the edges between the nodes are missing arrowheads. Is it possible (and preferably easy!) to display the edges as arrows in HoloViews?

I really want to be able to draw directed graphs like the D3 examples at https://bl.ocks.org/cjrd/6863459 and http://bl.ocks.org/rkirsling/5001347. But I'm struggling to find a Python visualization library that will allow me to do this.

[philippjfr]

Agreed it would be very nice if this supported. I think this is a good feature request and I've assigned it to the next release.

[cacti77]

Thanks! FYI I've asked the same question of Bokeh too. I gave up trying to do it with Plotly!

[jlstevens]

I think this would be a very valuable feature.

For a second I was wondering if you could overlay a vectorfield to achieve this. Unfortunately, even if you were to try such a desperate workaround, I don't think you would have access to the concrete layout of the edges to put the little vectors in the right places...

[philippjfr]

I considered something similar, namely that VectorField already implements code to draw arrows using the multi_line glyph so we could easily port that code and use it to draw directed edges in Graph.

[philippjfr]

Graphs now support a directed plot option which adds arrows indicating the directionality.

[cacti77]

Thanks very much!