neighborhood {KEGGgraph} | R Documentation

## Return the neighborhood set of given vertices

### Description

The function returns the neighborhood set of given vertices in the form of list. Optionally user can choose to include the given vertices in the list, too.

### Usage

    neighborhood(graph, index, return.self = FALSE)

### Arguments

`graph` | An object of `graphNEL`
`index` | Names of nodes, whose neighborhood set should be returned
`return.self` | logical, should the vertex itself also be returned?

### Details

Let v be a vertex in a (di)graph, the out-neighborhood or successor set (N+(v), x belongs to V(G) and v->x) and the in-neighborhood or predecessor set (N-(v), x belongs to V(G) and x->v) are jointly returned.

The returned list is indexed by the given node indices, `NULL` is returned in case of non-existing node.

The nodes are unique, that is, duplicated nodes are removed in results.

### Value

A list indexed by the given node indices, each entry containing the neighborhood set of that node (or furthermore including that node).

### Author(s)

Jitao David Zhang <jitao_david.zhang@roche.com>

### References

D.B. West. Introduction to Graph Theory, Second Edition. Prentice Hall, 2001

### Examples

      V <- c("Hamburg","Stuttgart","Berlin","Paris","Bremen")
      E <- list("Hamburg"=c("Berlin","Bremen"),
                "Stuttgart"=c("Berlin","Paris"),
                "Berlin"=c("Stuttgart","Bremen"),
                "Paris"=c("Stuttgart"),
                "Bremen"=c("Hamburg","Berlin"))
      g <- new("graphNEL", nodes=V, edgeL=E, edgemode="directed")
      if(require(Rgraphviz) & interactive()) {
        plot(g, "neato")
      }

      ## simple uses
      neighborhood(g, "Hamburg")
      neighborhood(g, c("Hamburg", "Berlin","Paris"))

      ## in case of non-existing nodes
      neighborhood(g, c("Stuttgart","Ulm"))

      ## also applicable to non-directed graphs
      neighborhood(ugraph(g), c("Stuttgart","Berlin"))

[Package KEGGgraph version 1.54.0 Index]