[igraph] Assign Weight to Link by Counting Repetitions

[Lorenzo Isella]

Dear All,
I often deal with graphs which are stored into files in the following form

174514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170
78774272 78774272
74514432 95879170

Do not be afraid of the long numbers; they are simply node labels used 
to construct an adjacency list.
Gabor pointed out that if these data are saved into 
graph_list_no_rep_dat, then I can read the graph as

> tab <- read.table("graph_list_no_rep_dat")
> g <- graph.data.frame(tab, dir=FALSE)
However, if you look at the graph above, you notice that some edges 
appear more than once and there are some self-loops.
Without going into details, this happens since this is a network 
aggregated over time.
By doing something like

g<-simplify(g)

I have a nice and clean graph without self-loops and repeated edges. It 
is OK for me to get rid of self-loops, but my only problem is that I 
would like to keep the info about how many times each edge used to 
appear and I would like to store this info as a weight associated to the 
edge itself.
Any suggestions about how to achieve that efficiently?
Many thanks

Lorenzo