How to get vertex ids back from graph
igraph, r
Solution
First of all, igraph uses the vertex attribute `name` as symbolic ids of vertices. I suggest you add the ids as `name` and use another name for the other attributes, e.g. `realname`.
But often you don't need to know the numeric ids if you are using symbolic names, because all functions accepts (well, they should) symbolic ids as well. E.g. if you want the degree of vertex `Peter`, you can just say `degree(g, "Peter")`.
If you really want the the numeric id, you can do things like these:
as.numeric(V(g)["Peter"])
# [1] 3
match("Peter", V(g)$name)
# [1] 3
If you want to get to `id` from `name` in your example, you can just index that vector with the result:
id[ match("Peter", V(g)$name) ]
Problem
Please consider the following ``` library(igraph) id <- c("1","2","A","B") name <- c("02 653245","03 4542342","Peter","Mary") category <- c("digit","digit","char","char") from <- c("1","1","2","A","A","B") to <- c("2","A","A","B","1","2") nodes <- cbind(id,name,category) edges <- cbind(from,to) g <- graph.data.frame(edges, directed=TRUE, vertices=nodes) ``` Now I want to access a specific vertex of the graph using the ids I used to create the graph from the data frame `id <- c("1","2","A","B")`. Let's say I want to access the third vertex - originally identified with "A". Is there any way to access the vertex with something like ``` V(g)$id == "A" ``` And is there anyway to obtain the `id` from `name`? That is, if I run ``` which(V(g)$name == "Peter") ``` I get `3`. How to get `A` instead?