shortest path outputs not properly

[masashi hashimoto]

Hi,

sp function outputs paths of node 3 - 1- 7 with weight of 16
but
path 3 - 4 - 7 has only weight of 5

is there any problem in my code ?

-------------code-------------------------------------------------------------------------------------------------------------

library(igraph)
#edge list
d <- data.frame(matrix(c( "2","1", "1","2", "2","0", "0","2", "3","2", "2","3", "3","1", "1","3", "4","3", "3","4", "4","0", "0","4", "5","0", "0","5", "5","3", "3","5", "6","5", "5","6", "6","1", "1","6", "7","1", "1","7", "7","4", "4","7", "8","7", "7","8", "8","1", "1","8", "9","1", "1","9", "9","2", "2","9", "0","7", "7","0", "0","1", "1","0", "1","5", "5","1"),nc=2,byrow=TRUE),stringsAsFactors=FALSE)
colnames(d) <- c("from","to")
#node list
vers <- data.frame(c("0","1","2","3","4","5","6","7","8","9"),stringsAsFactors=FALSE)
#create graph
g <- graph.data.frame(d,directed=TRUE,vertices=vers)
#weight
w1 <- c(3, 1, 8, 6, 2, 7, 8, 3, 3, 3, 7, 8, 1, 4, 3, 3, 1, 4, 8, 3, 1, 8, 6, 2, 7, 8, 3, 3, 3, 7, 8, 1, 4, 3, 3, 1, 4, 8)
E(g)$weight <- w1
#shortest path
sp <- get.shortest.paths(g,from=3,to=7)
sp
 c(c(d[[1]][7], d[[2]][7]),c(d[[1]][22],c(d[[2]][22])))
 E(g)$weight[[7]]+E(g)$weight[[22]]
 c(c(d[[1]][10], d[[2]][10]),c(d[[1]][24],c(d[[2]][24])))
 E(g)$weight[[10]]+E(g)$weight[[24]]

[Gábor Csárdi (gabor.csardi)]

You should use mode="out" if you want a directed path.

> get.shortest.paths(g, from=3, to=7, mode="out")
[[1]]
[1] 3 4 7

I agree that
- this is confusing
- it should be the default
- it should work properly, even if one uses mode="all"

So this is a bug.

[Gábor Csárdi (gabor.csardi)]

OK, it turns out that this is actually not really a bug. If you use mode="all", then edge directions are ignored, and there is a path 3-1-7, that has total weight 4. This is why you got that answer.

I have changed the default to mode="out", tought, in revision #1718 (0.6-main branch).

[Gábor Csárdi (gabor.csardi)]

And of course thanks for the report!

[Gábor Csárdi (gabor.csardi)]

The development of igraph has moved to github, so please do not comment on this bug here. You are of course welcome to comment on github, here:
https://github.com/igraph/igraph/issues/56