Re: [igraph] how to combine subgraphs with attributes

[Gabor Csardi]

Hi, ideally graph.union should handle edge attributes, it's a pity 
it doesn't. The quick and dirty solution for your example would be something 
like:

g <- graph.empty(n=11, directed=FALSE)
g <- add.edges(g, e1, color="red", sv=1)
g <- add.edges(g, e2, color="blue", sv=2)
g <- add.edges(g, e3, color="grey", sv=3)

A somewhat better solution is to write a function which steps through
all the graphs and their edge attributes to create the union graph:

my.union <- function(...) {
  graphs <- list(...)
  if (length(graphs)==0) {
     stop("Please supply at least one graph")
  }
  if (any(!sapply(graphs, is.igraph))) {
     stop("Not a graph object")
  }
  if (unique(sapply(graphs, is.directed))) {
     stop("You can't mix directed and undirected graphs")
  }

  v <- max(sapply(graphs, vcount))
  g <- graph.empty(n=v, directed=is.directed(graphs[[1]]))
  for (i in seq(along=graphs)) {
      attrnames <- list.edge.attributes(graphs[[i]])
      attrs <- list()
      for (j in attrnames) {
        attrs[[j]] <- get.edge.attribute(graphs[[i]], j)
      }
      g <- add.edges(g, t(get.edgelist(graphs[[i]])), attr=attrs)
  }
  g
}

and then you can write

g <- my.union(g1,g2,g3)

I haven't tested it too much....
Btw, for creating undirected graphs 

g1 <- graph(e1, directed=FALSE)

is better (clearer and faster) than 

g1 <- as.undirected(graph(e1))

Best,
Gabor

On Tue, Jul 03, 2007 at 12:01:14PM +0900, MATSUDA, Noriyuki wrote:
> Hello:
>    Can anyone help me combine subgraphs with specific attributes. 
> The following
> is a pilot script:
> -----------------------------------------------------------------------------------
> # BSJ07: Varying edge attribues by sigma
> #
> 
> e1<- c(0,1,1,2,2,3,3,4,4,10)) # sv1
> e2<- c(0,4,4,5,5,7,7,2)     # sv2
> e3<- c(3,8,8,4,4,0)         # sv3
> g1<-as.undirected(graph(e1))
> g2<-as.undirected(graph(e2))
> g3<-as.undirected(graph(e3))
> E(g1)$color <-"red"
> E(g2)$color <-"blue"
> E(g3)$color <-"grey"
> E(g1)$sv<-1
> E(g2)$sv<-2
> E(g3)$sv<-3
> 
> # g<- ??(g1,g2,g2)
> -----------------------------------------------------------------------------------
> 
>   An alternative is to create g out of e1,e2,e3 by
>      g<- as.undirected(graph( c(e1,e2,e3) )
> But, I need help in specifying its edge attributes depending on whether they
> originated from e1, e2 or e3.
> 
> Thanks in advance
> -- 
> 
> MATSUDA, Noriyuki, Ph.D.  Univ. of Tsukuba
> 
> 
> _______________________________________________
> igraph-help mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/igraph-help

-- 
Csardi Gabor <address@hidden>    MTA RMKI, ELTE TTK