Standard labeling of edges with integers {graph} | R Documentation

## Standard labeling of edges with integers

### Description

Functions to convert between from-to representation and standard labeling of the edges for undirected graphs with no self-loops.

### Usage

    ftM2int(ft)
    int2ftM(i)

### Arguments

`i` | Numeric vector.
`ft` | Numeric nx2 or 2xn matrix.

### Details

A standard 1-based node labeling of a graph G=(V,E) is a one-to-one mapping between the integers from 1 to |V| and the nodes in V. A standard 1-based edge labeling of an undirected graph G=(V,E) with no self-loops is the one-to-one mapping between the integers from 1 to |V| choose 2 = |V|*(|V|-1)/2 such that the edge labeled 1 is between nodes 2 and 1, the edge labeled 2 is between nodes 3 and 1, the edge labeled 3 is between nodes 3 and 2, and so on.

### Value

For `ftM2int`, a numeric vector of length n. For `int2ftM`, a `length(i) x 2` matrix.

### Author(s)

Wolfgang Huber

### Examples

     nNodes <- 200
     nEdges <- choose(nNodes, 2)
     i <- 1:nEdges
     ft <- int2ftM(i)
     ft[1:6,]
     stopifnot(all(ft[,1]>ft[,2])) ## always from higher to lower
     stopifnot(!any(duplicated(paste(ft[,1], ft[,2]))))
     stopifnot(ft[nEdges, 1]==nNodes, ft[nEdges, 2]==nNodes-1)

     j <- ftM2int(ft)
     stopifnot(all(i==j))

[Package graph version 1.72.0 Index]