[igraph] On ncol use and vertex labeling

[Anselmo Garcia Cantu Ros]

A big thank Tamasz for your quick reply!. The problem with the weights is 
fixed.
Now, if I got it right, read_graph_ncol() does not keep the labeling of the 
vertices, such as being specified in the input ncol-list. Could you please 
indicate me what would be the best way to reassign the original ID's to the 
graph vertices.
Moreover, if i decided to use "ncol" edge-lists, it is because the sizes of 
the weighted networks that am analyzing seem to be too large for creating 
matrices. May be you can suggest me a better approach to get around with 
the size difficulty right from the start. 

Thanks again, 

Anselmo. 

Tamás Nepusz writes: 

> Hello, 
>
> You have to specify the name of the edge attribute you want to read the weights from. The easiest way to do it is as follows: 
>
> const char *weight = "weight"; 
>
> Then simply proceed with igraph_cattribute_EANV as above. Note that EANV in macro for is a shorthand for igraph_cattribute_EANV, see: 
>
> http://igraph.sourceforge.net/doc/html/ch09s02s01.html#EANV 
>
> --
> T.
> On Tuesday, 5 July 2011 at 19:14, Anselmo Garcia Cantu Ros wrote: 
> > Hi,  
> >
> > I am debuting in igraph and am using c igraph 0.6.
> > I need to calculate distances within weighted graphs. Thus I've built the 
> > graph from a weighted adjacency matrix, and then used 
> > igraph_shortest_paths_dijkstra(). Everything was fine until working with 
> > graph sizes of the order 10^4: Out of memory (apparently, the size was too 
> > big for matrix). To overcome this situation I decided to build up the 
> > graphs from a 3-column adjacency list (in format .ncol), that was fed into 
> > "igraph_read_graph_ncol()". The edge query was done again using 
> > igraph_cattribute_EANV(). When executing I get:  
> >
> > "Error at cattributes.c:1915 :Unknown attribute, Invalid value"  
> >
> > Please help me. The code is the following:  
> >
> > #include <igraph/igraph.h>
> > #include <stdio.h>
> > int main(void) {
> >  FILE *fp;
> >  fp=fopen("Matrixoutweight.ncol","r");  
> >
> >  igraph_i_set_attribute_table(&igraph_cattribute_table);  
> >
> >  igraph_t graph; 
> >
> >  int i,j,nedges,nertex;
> >  float test;
> >  const char weight;  
> >
> > igraph_read_graph_ncol(&graph,fp,NULL,0,1,0);  
> >
> >  nedges=igraph_ecount(&graph);
> >  nertex=igraph_vcount(&graph);  
> >
> >  igraph_vector_t weightatt;
> >  igraph_vector_init(&weightatt,nedges);
> >  igraph_matrix_t SP;
> >  igraph_matrix_init(&SP,nertex,nertex);  
> >
> >  igraph_cattribute_EANV(&graph,&weight,igraph_ess_all(IGRAPH_EDGEORDER_FROM)
> > , &weightatt); 
> >
> >
> >  igraph_shortest_paths_dijkstra(&graph,&SP,igraph_vss_all(),igraph_vss_all()
> > ,&weightatt,IGRAPH_OUT);  
> >
> >  for (i = 0; i < nertex ; i++)
> >  {
> >  for (j = 0; j < nertex; j++)
> >  {
> >  test=igraph_matrix_e(&SP,i,j);
> >  printf("%d %d %f\n",i,j,test);
> >  }
> >  } 
> >
> >  igraph_destroy(&graph);
> >  igraph_vector_destroy(&weightatt);
> >  igraph_matrix_destroy(&SP); 
> >
> >  fclose(fp); 
> >
> >  return 0;
> > }  
> >
> > Thanks in advance 
> >
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