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## Re: [igraph] how to combine subgraphs with attributes

 From: MATSUDA, Noriyuki Subject: Re: [igraph] how to combine subgraphs with attributes Date: Tue, 3 Jul 2007 18:17:57 +0900

```Hi Garbar:

Thank you for the prompt rescue.

At 11:00 AM +0200 07.7.3, Gabor Csardi wrote:
```
```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
}

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.

--

MATSUDA, Noriyuki, Ph.D.  Univ. of Tsukuba

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

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```
```

--

Prof. MATSUDA, Noriyuki, Ph.D.  Univ. of Tsukuba
Grad. Sch. of Sys. & Info. Eng.  Dept. of Social Systems & Management
(In Kanji ) 松 田 紀 之，筑波大学大学院教授
システム情報工学研究科 社会システム・マネジメント専攻

```