Re: [igraph] grid graphs

[Raphael C]

Thank you.  How can I then persuade igraph to plot the graph on a 2d
grid maintaining the original position of the nodes?

Raphael

On 11 November 2013 21:36, Tamás Nepusz <address@hidden> wrote:
> Hi,
>
> Suppose that you have an N x M grid (N rows, M columns). In this case, you
> can simply convert from an (x,y) index pair to an integer node ID with the
> following function:
>
> def grid_coords_to_index(x, y):
>     return (y-1)*M + (x-1)
>
> and vice versa:
>
> def index_to_grid_coords(index):
>     y, x = divmod(index, M)
>     return x+1, y+1
>
> Note that I’m assuming 1-based grid coords since your example seems to imply
> that. Then you can use the first function above to convert your edge list
> given in grid coords to an edge list given in vertex indices.
>
> --
> T.
>
> On Monday, 11 November 2013 at 22:28, Raphael C wrote:
>
> Hi,
>
> I have a graph laid out on a 2d graph. Some edges are included in the
> graph and some not. The edges are represented as lists of
> ((x1,y1),(x2,y2)) as in the following example of a complete graph
> description,
>
> edges = [((1, 1), (2, 1)), ((2, 1), (3, 1)), ((3, 1), (4, 1)),
> ((3, 2), (4, 2)), ((3, 5), (4, 5)), ((4, 1), (5, 1)), ((4, 2), (5,
> 2)), ((4, 5), (5, 5)), ((1, 1), (1, 2)), ((3, 1), (3, 2)), ((4, 1),
> (4, 2)), ((5, 1), (5, 2)), ((5, 2), (5, 3)), ((5, 3), (5, 4)), ((5,
> 4), (5, 5))]
>
> What is a simple way to make an undirected igraph graph from this
> list? I need to be able to have the nodes labelled by their `(x,y)`
> positions.
>
> I would like to be able to plot this graph on a grid too so ideally it
> would maintain the positions of the nodes.
>
> I am working in python.
>
> Thanks for any help.
> Raphael
>
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