Drawing properties (newbie question)

graph-tool
1

Hello,

I'm a newcomer to Python and I don't understand the way I could get drawn
some properties for edges or vertices.

The documentation says:

vprops : dict (default: {})

    Additional vertex properties, as a dictionary. The keys are the property
names, and the values must be convertible to string, or vertex property
maps, with values convertible to strings.

But I guess that I'm missing something with Python as I only get drawn a
text description of the object. Foe example:

If I try a sentence like

graph_draw(g, eprops={"label": g.edge_properties}, output="two-nodes2.png")

it draws obviously the label for that object which is:

{'occ': <PropertyMap object with key type 'Edge' and value type
'int32_t', for Graph 0x2f6dcd0, at 0x2f6de10>}

But I don't understand which parameter I should pass to graph_draw in order
to get the desired outcome.

Could you provide a mini-example of drawing a small graph with properties on
edges/vertices? This could also be added to the Quick tutorial.

Thank you in advance peers.

Regards.

2

Hi Gustav,

If I try a sentence like

graph_draw(g, eprops={"label": g.edge_properties}, output="two-nodes2.png")

it draws obviously the label for that object which is:

{'occ': <PropertyMap object with key type 'Edge' and value type
'int32_t', for Graph 0x2f6dcd0, at 0x2f6de10>}

But I don't understand which parameter I should pass to graph_draw in order
to get the desired outcome.

The attribute g.edge_properties is a dictionary of internal property
maps. What you want to so is to pass some property map in isolation, not
all of them. What you want to pass depends of course of what you want to
do, which is not very clear to me.

Suppose, for instance, you have a property map which has numeric value
for each edge, which is called "edge_prop", which is created as such:

    edge_prop = g.new_edge_property("double")
    for e in g.edges():
        edge_prop[e] = random() # fill with random values

If you want to draw a label on top of the edges with these values you
would do:

   graph_draw(g, eprops={"label": edge_prop})

If, instead you want it to represent the length of the edge, you would do
something like:

   graph_draw(g, eprops={"len": edge_prop})

Take a look at Attributes | Graphviz for all
possible properties one can set.

Note that for vertex and edge color, as well as size, graph_draw()
provides direct parameters, so one does not need to pass anything to
eprops or vprops.

Cheers,
Tiago

3

Hello,

Thank you Tiago.

I think I got it now. I was misunderstanding those "label"/"len" parametres
as something within the dictionary when in fact they are refering to
properties in GraphViz.

I'll make some tests and if I'll have some doubts yet I'll be back.

Thanks again.

Regards.