0

I have a question, how to find path between nodes in R if weigths are sometimes negative? I tried first with finding the shortest path (found a post here Find distance of route from get.shortest.paths()), but an error appears: 

Error in .Call("R_igraph_get_shortest_paths", graph, as.igraph.vs(graph,  : 
  At structural_properties.c:4406 : Weight vector must be non-negative, Invalid value

Below i put the code which I used and the beginning of the dataset. Equally I would appreciate if sb could give me a tip how to find a longest route in a tree.

install.packages("igraph")
library(igraph)

start_id <- base.set$id.parent
end_id <- base.set$id
value <- base.set$value
tree <- as.data.frame(cbind(start_id, end_id, value))

gtree <- graph.data.frame(tree[-1,],directed=F)
class(tree)
tkplot(gtree)
E(gtree)

print(gtree, e=TRUE, v=TRUE)


## calculate shortest path between vertex 234 and 245
(tmp2 = get.shortest.paths(gtree, from='234', to='245',weights=E(gtree)$value))

# compute the min distances from '234' to all other vertices
tmp3 <- shortest.paths(g2,v='234',weights=E(g2)$value)

# print min distance from '234' to '245'
tmp3[1, which(V(g2)$name == '245')]

###data set
   start_id end_id  value
1   NA         0    0.000000000
2   0          1    -0.372677962
3   0          2    0.250537488
4   0          3    0.580284747
5   0          4    -0.674850541
6   0          5    1.958636421
7   0          6    -2.651893647
8   0          7    0.072457405
9   1          8    -0.357686434
10  1          9    -0.934105631
11  1          10   -0.752714220
12  1          11   -1.068627403
13  2          12   -0.281384892
14  2          13   -1.264358146
15  2          14   -1.043058993
16  2          15   -0.409834522
17  3          16   -0.302880563
18  3          17   -0.423105784
19  3          18   1.104676924
20  3          19   -0.497643735
21  3          20   -2.280475263
22  3          21   1.316331335
23  3   22  -1.143292548
Community
  • 1
  • 1
user3463225
  • 401
  • 9
  • 19
  • Please clean up your example. The data you provided appears to be for the `tree` object so the way in which you created that is irrelevant. The to/from values you use in your sample aren't in the sample data. You reference on object `g2` which is not defined. The data you proved appears to have negative cycles. This means you can continual make the "total distance" shorter by walking infinitely in loop so there is no "shortest" path. – MrFlick May 26 '15 at 20:36
  • so can u help me how should I load this data in R to define it as a tree? – user3463225 May 28 '15 at 04:50

0 Answers0