# combineNodes: combineNodes In graph: graph: A package to handle graph data structures

## Description

A function to combine, or collapse, a specified set of nodes in a graph.

## Usage

 ```1 2 3``` ```combineNodes(nodes, graph, newName, ...) ## S4 method for signature 'character,graphNEL,character' combineNodes(nodes, graph, newName, collapseFunction=sum) ```

## Arguments

 `nodes` A set of nodes that are to be collapsed. `graph` The graph containing the nodes `newName` The name for the new, collapsed node. `collapseFunction` Function or character giving the name of a function used to collapse the edge weights after combining nodes. The default is to sum up the weights, but mean would be a useful alternative. `...` Additional arguments for the generic

## Details

The nodes specified are reduced to a single new node with label given by `newName`. The in and out edges of the set of nodes are all made into in and out edges for the new node.

## Value

An new instance of a graph of the same class as `graph` is returned. This new graph has the specified nodes reduced to a single node.

## Author(s)

R. Gentleman

`inEdges`, `addNode`
 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15``` ``` V <- LETTERS[1:4] edL1 <- vector("list", length=4) names(edL1) <- V for(i in 1:4) edL1[[i]] <- list(edges=c(2,1,4,3)[i], weights=sqrt(i)) gR <- graphNEL(nodes=V, edgeL=edL1, edgemode="directed") gR <- addNode("M", gR) gR <- addEdge("M", "A", gR, 1) gR <- addEdge("B", "D", gR, 1) gX <- combineNodes(c("B","D"), gR, "X") gR <- addNode("K", gR) gR <- addEdge(c("K","K"), c("D", "B"), gR, c(5,3)) edgeWeights(combineNodes(c("B","D"), gR, "X"))\$K edgeWeights(combineNodes(c("B","D"), gR, "X", mean))\$K ```