|Subject:||Re: [igraph] Question on max id node|
|Date:||Tue, 11 Mar 2008 13:38:32 -0400|
|User-agent:||Thunderbird 220.127.116.11 (X11/20080227)|
Thanks for the description of vertex id's vs vertex attributes... it did clear things up for me.
I think I was misusing the the term 'id' from the igraph point of view. I really should have used the the term 'name attribute'.
The name attribute makes for a good reference back to the graph originally imported, and when using non-igraph routines and looking for intermediate verification, a fixed reference such as the vertex name attribute can make life easier.
Gabor Csardi wrote:
Ok, so we know the reason at least. I'll see what i can do to correct this. Some more clarification about vertex ids/attributes. In every igraph graph, vertices have numeric ids starting with zero, up to number_of_nodes-1. This is always true, e.g. if you delete some vertices then the ids are renumbered. Think of the vertices as balls in a tube, one after the another, the ids are the _positions_ of the balls. Vertex attributes are arbitrary labels atteched to vertices. Vertex attributes are preserved. E.g. if a graph has vertex attribute named "foo" and vertex 3 (internal, position 3) has "foo" value "foobar", and you remove vertex 2 from this graph, then vertex 3 becomes vertex 2 (although you should not rely on the ordering being kept), but it's "foo" attribute will be still "foobar". ..._edgelist interprets the numbers in the file as internal vertex ids. The number of vertices in the graph will be set to the highest id+1. E.g. if you have only 99 100 in your file, then the number of vertices will be 101, and 99 vertices will be isolate. ..._ncol interprets the _strings_ in the file as vertex labels, and one vertex is created for each label. I.e. for the same one line file, a graph with two vertices is created (internal ids 0 and 1) and their "name" attributes will be set to "99" and "100", respectively. Now that i think back, why do you need the attributes? The subject of this email is (still) "...max id node". So if you need the max. internal id, that is always vcount()-1. Hope it is clear now, G. On Mon, Mar 10, 2008 at 08:00:44PM -0400, Richard Geddes wrote:G, I think the problem is in the file format end-of-line character of the file, which originally was made on a windows machine.� I converted the dos format to linux with tr -d '\r' < dos.pairs > linux.pairs and results are consistent now.� I've attached the file in question (dos.pairs) and the linux version so you can verify. I had this problem not too long ago with some scripting code I was writing and should have suspected the same was happening here. ... I ran the update routine: $0> cd (path to)igraph-dev-0.6 $0> tla update $0> ./bootstrap.sh $0> ./configure $0> make $0> sudo make install The 'make check' returned a value of 0 (good) Yes, I follow about the internal renaming of the nodes... Is the attribute method the best method to get at the internal igraph node id values... I didn't really get to that part yet. R
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